"""Unit tests for collections.py."""

import array
import collections
import copy
import doctest
import inspect
import operator
import pickle
from random import choice, randrange
from itertools import product, chain, combinations
import string
import sys
from test import support
from test.support.import_helper import import_fresh_module
import types
import unittest

from collections import namedtuple, Counter, OrderedDict, _count_elements
from collections import UserDict, UserString, UserList
from collections import ChainMap
from collections import deque
from collections.abc import Awaitable, Coroutine
from collections.abc import AsyncIterator, AsyncIterable, AsyncGenerator
from collections.abc import Hashable, Iterable, Iterator, Generator, Reversible
from collections.abc import Sized, Container, Callable, Collection
from collections.abc import Set, MutableSet
from collections.abc import Mapping, MutableMapping, KeysView, ItemsView, ValuesView
from collections.abc import Sequence, MutableSequence
from collections.abc import Buffer


class TestUserObjects(unittest.TestCase):
    def _superset_test(self, a, b):
        self.assertGreaterEqual(
            set(dir(a)),
            set(dir(b)),
            '{a} should have all the methods of {b}'.format(
                a=a.__name__,
                b=b.__name__,
            ),
        )

    def _copy_test(self, obj):
        # Test internal copy
        obj_copy = obj.copy()
        self.assertIsNot(obj.data, obj_copy.data)
        self.assertEqual(obj.data, obj_copy.data)

        # Test copy.copy
        obj.test = [1234]  # Make sure instance vars are also copied.
        obj_copy = copy.copy(obj)
        self.assertIsNot(obj.data, obj_copy.data)
        self.assertEqual(obj.data, obj_copy.data)
        self.assertIs(obj.test, obj_copy.test)

    def test_str_protocol(self):
        self._superset_test(UserString, str)

    def test_list_protocol(self):
        self._superset_test(UserList, list)

    def test_dict_protocol(self):
        self._superset_test(UserDict, dict)

    def test_list_copy(self):
        obj = UserList()
        obj.append(123)
        self._copy_test(obj)

    def test_dict_copy(self):
        obj = UserDict()
        obj[123] = "abc"
        self._copy_test(obj)

    def test_dict_missing(self):
        class A(UserDict):
            def __missing__(self, key):
                return 456
        self.assertEqual(A()[123], 456)
        # get() ignores __missing__ on dict
        self.assertIs(A().get(123), None)


################################################################################
### ChainMap (helper class for configparser and the string module)
################################################################################

class TestChainMap(unittest.TestCase):

    def test_basics(self):
        c = ChainMap()
        c['a'] = 1
        c['b'] = 2
        d = c.new_child()
        d['b'] = 20
        d['c'] = 30
        self.assertEqual(d.maps, [{'b':20, 'c':30}, {'a':1, 'b':2}])  # check internal state
        self.assertEqual(d.items(), dict(a=1, b=20, c=30).items())    # check items/iter/getitem
        self.assertEqual(len(d), 3)                                   # check len
        for key in 'abc':                                             # check contains
            self.assertIn(key, d)
        for k, v in dict(a=1, b=20, c=30, z=100).items():             # check get
            self.assertEqual(d.get(k, 100), v)

        del d['b']                                                    # unmask a value
        self.assertEqual(d.maps, [{'c':30}, {'a':1, 'b':2}])          # check internal state
        self.assertEqual(d.items(), dict(a=1, b=2, c=30).items())     # check items/iter/getitem
        self.assertEqual(len(d), 3)                                   # check len
        for key in 'abc':                                             # check contains
            self.assertIn(key, d)
        for k, v in dict(a=1, b=2, c=30, z=100).items():              # check get
            self.assertEqual(d.get(k, 100), v)
        self.assertIn(repr(d), [                                      # check repr
            type(d).__name__ + "({'c': 30}, {'a': 1, 'b': 2})",
            type(d).__name__ + "({'c': 30}, {'b': 2, 'a': 1})"
        ])

        for e in d.copy(), copy.copy(d):                               # check shallow copies
            self.assertEqual(d, e)
            self.assertEqual(d.maps, e.maps)
            self.assertIsNot(d, e)
            self.assertIsNot(d.maps[0], e.maps[0])
            for m1, m2 in zip(d.maps[1:], e.maps[1:]):
                self.assertIs(m1, m2)

        # check deep copies
        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
            e = pickle.loads(pickle.dumps(d, proto))
            self.assertEqual(d, e)
            self.assertEqual(d.maps, e.maps)
            self.assertIsNot(d, e)
            for m1, m2 in zip(d.maps, e.maps):
                self.assertIsNot(m1, m2, e)
        for e in [copy.deepcopy(d),
                  eval(repr(d))
                ]:
            self.assertEqual(d, e)
            self.assertEqual(d.maps, e.maps)
            self.assertIsNot(d, e)
            for m1, m2 in zip(d.maps, e.maps):
                self.assertIsNot(m1, m2, e)

        f = d.new_child()
        f['b'] = 5
        self.assertEqual(f.maps, [{'b': 5}, {'c':30}, {'a':1, 'b':2}])
        self.assertEqual(f.parents.maps, [{'c':30}, {'a':1, 'b':2}])   # check parents
        self.assertEqual(f['b'], 5)                                    # find first in chain
        self.assertEqual(f.parents['b'], 2)                            # look beyond maps[0]

    def test_ordering(self):
        # Combined order matches a series of dict updates from last to first.
        # This test relies on the ordering of the underlying dicts.

        baseline = {'music': 'bach', 'art': 'rembrandt'}
        adjustments = {'art': 'van gogh', 'opera': 'carmen'}

        cm = ChainMap(adjustments, baseline)

        combined = baseline.copy()
        combined.update(adjustments)

        self.assertEqual(list(combined.items()), list(cm.items()))

    def test_constructor(self):
        self.assertEqual(ChainMap().maps, [{}])                        # no-args --> one new dict
        self.assertEqual(ChainMap({1:2}).maps, [{1:2}])                # 1 arg --> list

    def test_bool(self):
        self.assertFalse(ChainMap())
        self.assertFalse(ChainMap({}, {}))
        self.assertTrue(ChainMap({1:2}, {}))
        self.assertTrue(ChainMap({}, {1:2}))

    def test_missing(self):
        class DefaultChainMap(ChainMap):
            def __missing__(self, key):
                return 999
        d = DefaultChainMap(dict(a=1, b=2), dict(b=20, c=30))
        for k, v in dict(a=1, b=2, c=30, d=999).items():
            self.assertEqual(d[k], v)                                  # check __getitem__ w/missing
        for k, v in dict(a=1, b=2, c=30, d=77).items():
            self.assertEqual(d.get(k, 77), v)                          # check get() w/ missing
        for k, v in dict(a=True, b=True, c=True, d=False).items():
            self.assertEqual(k in d, v)                                # check __contains__ w/missing
        self.assertEqual(d.pop('a', 1001), 1, d)
        self.assertEqual(d.pop('a', 1002), 1002)                       # check pop() w/missing
        self.assertEqual(d.popitem(), ('b', 2))                        # check popitem() w/missing
        with self.assertRaises(KeyError):
            d.popitem()

    def test_order_preservation(self):
        d = ChainMap(
                OrderedDict(j=0, h=88888),
                OrderedDict(),
                OrderedDict(i=9999, d=4444, c=3333),
                OrderedDict(f=666, b=222, g=777, c=333, h=888),
                OrderedDict(),
                OrderedDict(e=55, b=22),
                OrderedDict(a=1, b=2, c=3, d=4, e=5),
                OrderedDict(),
            )
        self.assertEqual(''.join(d), 'abcdefghij')
        self.assertEqual(list(d.items()),
            [('a', 1), ('b', 222), ('c', 3333), ('d', 4444),
             ('e', 55), ('f', 666), ('g', 777), ('h', 88888),
             ('i', 9999), ('j', 0)])

    def test_iter_not_calling_getitem_on_maps(self):
        class DictWithGetItem(UserDict):
            def __init__(self, *args, **kwds):
                self.called = False
                UserDict.__init__(self, *args, **kwds)
            def __getitem__(self, item):
                self.called = True
                UserDict.__getitem__(self, item)

        d = DictWithGetItem(a=1)
        c = ChainMap(d)
        d.called = False

        set(c)  # iterate over chain map
        self.assertFalse(d.called, '__getitem__ was called')

    def test_dict_coercion(self):
        d = ChainMap(dict(a=1, b=2), dict(b=20, c=30))
        self.assertEqual(dict(d), dict(a=1, b=2, c=30))
        self.assertEqual(dict(d.items()), dict(a=1, b=2, c=30))

    def test_new_child(self):
        'Tests for changes for issue #16613.'
        c = ChainMap()
        c['a'] = 1
        c['b'] = 2
        m = {'b':20, 'c': 30}
        d = c.new_child(m)
        self.assertEqual(d.maps, [{'b':20, 'c':30}, {'a':1, 'b':2}])  # check internal state
        self.assertIs(m, d.maps[0])

        # Use a different map than a dict
        class lowerdict(dict):
            def __getitem__(self, key):
                if isinstance(key, str):
                    key = key.lower()
                return dict.__getitem__(self, key)
            def __contains__(self, key):
                if isinstance(key, str):
                    key = key.lower()
                return dict.__contains__(self, key)

        c = ChainMap()
        c['a'] = 1
        c['b'] = 2
        m = lowerdict(b=20, c=30)
        d = c.new_child(m)
        self.assertIs(m, d.maps[0])
        for key in 'abc':                                             # check contains
            self.assertIn(key, d)
        for k, v in dict(a=1, B=20, C=30, z=100).items():             # check get
            self.assertEqual(d.get(k, 100), v)

        c = ChainMap({'a': 1, 'b': 2})
        d = c.new_child(b=20, c=30)
        self.assertEqual(d.maps, [{'b': 20, 'c': 30}, {'a': 1, 'b': 2}])

    def test_union_operators(self):
        cm1 = ChainMap(dict(a=1, b=2), dict(c=3, d=4))
        cm2 = ChainMap(dict(a=10, e=5), dict(b=20, d=4))
        cm3 = cm1.copy()
        d = dict(a=10, c=30)
        pairs = [('c', 3), ('p',0)]

        tmp = cm1 | cm2 # testing between chainmaps
        self.assertEqual(tmp.maps, [cm1.maps[0] | dict(cm2), *cm1.maps[1:]])
        cm1 |= cm2
        self.assertEqual(tmp, cm1)

        tmp = cm2 | d # testing between chainmap and mapping
        self.assertEqual(tmp.maps, [cm2.maps[0] | d, *cm2.maps[1:]])
        self.assertEqual((d | cm2).maps, [d | dict(cm2)])
        cm2 |= d
        self.assertEqual(tmp, cm2)

        # testing behavior between chainmap and iterable key-value pairs
        with self.assertRaises(TypeError):
            cm3 | pairs
        tmp = cm3.copy()
        cm3 |= pairs
        self.assertEqual(cm3.maps, [tmp.maps[0] | dict(pairs), *tmp.maps[1:]])

        # testing proper return types for ChainMap and it's subclasses
        class Subclass(ChainMap):
            pass

        class SubclassRor(ChainMap):
            def __ror__(self, other):
                return super().__ror__(other)

        tmp = ChainMap() | ChainMap()
        self.assertIs(type(tmp), ChainMap)
        self.assertIs(type(tmp.maps[0]), dict)
        tmp = ChainMap() | Subclass()
        self.assertIs(type(tmp), ChainMap)
        self.assertIs(type(tmp.maps[0]), dict)
        tmp = Subclass() | ChainMap()
        self.assertIs(type(tmp), Subclass)
        self.assertIs(type(tmp.maps[0]), dict)
        tmp = ChainMap() | SubclassRor()
        self.assertIs(type(tmp), SubclassRor)
        self.assertIs(type(tmp.maps[0]), dict)


################################################################################
### Named Tuples
################################################################################

TestNT = namedtuple('TestNT', 'x y z')    # type used for pickle tests

class TestNamedTuple(unittest.TestCase):

    def test_factory(self):
        Point = namedtuple('Point', 'x y')
        self.assertEqual(Point.__name__, 'Point')
        self.assertEqual(Point.__slots__, ())
        self.assertEqual(Point.__module__, __name__)
        self.assertEqual(Point.__getitem__, tuple.__getitem__)
        self.assertEqual(Point._fields, ('x', 'y'))

        self.assertRaises(ValueError, namedtuple, 'abc%', 'efg ghi')       # type has non-alpha char
        self.assertRaises(ValueError, namedtuple, 'class', 'efg ghi')      # type has keyword
        self.assertRaises(ValueError, namedtuple, '9abc', 'efg ghi')       # type starts with digit

        self.assertRaises(ValueError, namedtuple, 'abc', 'efg g%hi')       # field with non-alpha char
        self.assertRaises(ValueError, namedtuple, 'abc', 'abc class')      # field has keyword
        self.assertRaises(ValueError, namedtuple, 'abc', '8efg 9ghi')      # field starts with digit
        self.assertRaises(ValueError, namedtuple, 'abc', '_efg ghi')       # field with leading underscore
        self.assertRaises(ValueError, namedtuple, 'abc', 'efg efg ghi')    # duplicate field

        namedtuple('Point0', 'x1 y2')   # Verify that numbers are allowed in names
        namedtuple('_', 'a b c')        # Test leading underscores in a typename

        nt = namedtuple('nt', 'the quick brown fox')                       # check unicode input
        self.assertNotIn("u'", repr(nt._fields))
        nt = namedtuple('nt', ('the', 'quick'))                           # check unicode input
        self.assertNotIn("u'", repr(nt._fields))

        self.assertRaises(TypeError, Point._make, [11])                     # catch too few args
        self.assertRaises(TypeError, Point._make, [11, 22, 33])             # catch too many args

    def test_defaults(self):
        Point = namedtuple('Point', 'x y', defaults=(10, 20))              # 2 defaults
        self.assertEqual(Point._field_defaults, {'x': 10, 'y': 20})
        self.assertEqual(Point(1, 2), (1, 2))
        self.assertEqual(Point(1), (1, 20))
        self.assertEqual(Point(), (10, 20))

        Point = namedtuple('Point', 'x y', defaults=(20,))                 # 1 default
        self.assertEqual(Point._field_defaults, {'y': 20})
        self.assertEqual(Point(1, 2), (1, 2))
        self.assertEqual(Point(1), (1, 20))

        Point = namedtuple('Point', 'x y', defaults=())                     # 0 defaults
        self.assertEqual(Point._field_defaults, {})
        self.assertEqual(Point(1, 2), (1, 2))
        with self.assertRaises(TypeError):
            Point(1)

        with self.assertRaises(TypeError):                                  # catch too few args
            Point()
        with self.assertRaises(TypeError):                                  # catch too many args
            Point(1, 2, 3)
        with self.assertRaises(TypeError):                                  # too many defaults
            Point = namedtuple('Point', 'x y', defaults=(10, 20, 30))
        with self.assertRaises(TypeError):                                  # non-iterable defaults
            Point = namedtuple('Point', 'x y', defaults=10)
        with self.assertRaises(TypeError):                                  # another non-iterable default
            Point = namedtuple('Point', 'x y', defaults=False)

        Point = namedtuple('Point', 'x y', defaults=None)                   # default is None
        self.assertEqual(Point._field_defaults, {})
        self.assertIsNone(Point.__new__.__defaults__, None)
        self.assertEqual(Point(10, 20), (10, 20))
        with self.assertRaises(TypeError):                                  # catch too few args
            Point(10)

        Point = namedtuple('Point', 'x y', defaults=[10, 20])               # allow non-tuple iterable
        self.assertEqual(Point._field_defaults, {'x': 10, 'y': 20})
        self.assertEqual(Point.__new__.__defaults__, (10, 20))
        self.assertEqual(Point(1, 2), (1, 2))
        self.assertEqual(Point(1), (1, 20))
        self.assertEqual(Point(), (10, 20))

        Point = namedtuple('Point', 'x y', defaults=iter([10, 20]))         # allow plain iterator
        self.assertEqual(Point._field_defaults, {'x': 10, 'y': 20})
        self.assertEqual(Point.__new__.__defaults__, (10, 20))
        self.assertEqual(Point(1, 2), (1, 2))
        self.assertEqual(Point(1), (1, 20))
        self.assertEqual(Point(), (10, 20))

    def test_readonly(self):
        Point = namedtuple('Point', 'x y')
        p = Point(11, 22)
        with self.assertRaises(AttributeError):
            p.x = 33
        with self.assertRaises(AttributeError):
            del p.x
        with self.assertRaises(TypeError):
            p[0] = 33
        with self.assertRaises(TypeError):
            del p[0]
        self.assertEqual(p.x, 11)
        self.assertEqual(p[0], 11)

    @unittest.skipIf(sys.flags.optimize >= 2,
                     "Docstrings are omitted with -O2 and above")
    def test_factory_doc_attr(self):
        Point = namedtuple('Point', 'x y')
        self.assertEqual(Point.__doc__, 'Point(x, y)')
        Point.__doc__ = '2D point'
        self.assertEqual(Point.__doc__, '2D point')

    @unittest.skipIf(sys.flags.optimize >= 2,
                     "Docstrings are omitted with -O2 and above")
    def test_field_doc(self):
        Point = namedtuple('Point', 'x y')
        self.assertEqual(Point.x.__doc__, 'Alias for field number 0')
        self.assertEqual(Point.y.__doc__, 'Alias for field number 1')
        Point.x.__doc__ = 'docstring for Point.x'
        self.assertEqual(Point.x.__doc__, 'docstring for Point.x')
        # namedtuple can mutate doc of descriptors independently
        Vector = namedtuple('Vector', 'x y')
        self.assertEqual(Vector.x.__doc__, 'Alias for field number 0')
        Vector.x.__doc__ = 'docstring for Vector.x'
        self.assertEqual(Vector.x.__doc__, 'docstring for Vector.x')

    @support.cpython_only
    @unittest.skipIf(sys.flags.optimize >= 2,
                     "Docstrings are omitted with -O2 and above")
    def test_field_doc_reuse(self):
        P = namedtuple('P', ['m', 'n'])
        Q = namedtuple('Q', ['o', 'p'])
        self.assertIs(P.m.__doc__, Q.o.__doc__)
        self.assertIs(P.n.__doc__, Q.p.__doc__)

    @support.cpython_only
    def test_field_repr(self):
        Point = namedtuple('Point', 'x y')
        self.assertEqual(repr(Point.x), "_tuplegetter(0, 'Alias for field number 0')")
        self.assertEqual(repr(Point.y), "_tuplegetter(1, 'Alias for field number 1')")

        Point.x.__doc__ = 'The x-coordinate'
        Point.y.__doc__ = 'The y-coordinate'

        self.assertEqual(repr(Point.x), "_tuplegetter(0, 'The x-coordinate')")
        self.assertEqual(repr(Point.y), "_tuplegetter(1, 'The y-coordinate')")

    def test_name_fixer(self):
        for spec, renamed in [
            [('efg', 'g%hi'),  ('efg', '_1')],                              # field with non-alpha char
            [('abc', 'class'), ('abc', '_1')],                              # field has keyword
            [('8efg', '9ghi'), ('_0', '_1')],                               # field starts with digit
            [('abc', '_efg'), ('abc', '_1')],                               # field with leading underscore
            [('abc', 'efg', 'efg', 'ghi'), ('abc', 'efg', '_2', 'ghi')],    # duplicate field
            [('abc', '', 'x'), ('abc', '_1', 'x')],                         # fieldname is a space
        ]:
            self.assertEqual(namedtuple('NT', spec, rename=True)._fields, renamed)

    def test_module_parameter(self):
        NT = namedtuple('NT', ['x', 'y'], module=collections)
        self.assertEqual(NT.__module__, collections)

    def test_instance(self):
        Point = namedtuple('Point', 'x y')
        p = Point(11, 22)
        self.assertEqual(p, Point(x=11, y=22))
        self.assertEqual(p, Point(11, y=22))
        self.assertEqual(p, Point(y=22, x=11))
        self.assertEqual(p, Point(*(11, 22)))
        self.assertEqual(p, Point(**dict(x=11, y=22)))
        self.assertRaises(TypeError, Point, 1)          # too few args
        self.assertRaises(TypeError, Point, 1, 2, 3)    # too many args
        with self.assertRaises(TypeError):              # wrong keyword argument
            Point(XXX=1, y=2)
        with self.assertRaises(TypeError):              # missing keyword argument
            Point(x=1)
        self.assertEqual(repr(p), 'Point(x=11, y=22)')
        self.assertNotIn('__weakref__', dir(p))
        self.assertEqual(p, Point._make([11, 22]))      # test _make classmethod
        self.assertEqual(p._fields, ('x', 'y'))         # test _fields attribute
        self.assertEqual(p._replace(x=1), (1, 22))      # test _replace method
        self.assertEqual(p._asdict(), dict(x=11, y=22)) # test _asdict method

        with self.assertRaises(TypeError):
            p._replace(x=1, error=2)

        # verify that field string can have commas
        Point = namedtuple('Point', 'x, y')
        p = Point(x=11, y=22)
        self.assertEqual(repr(p), 'Point(x=11, y=22)')

        # verify that fieldspec can be a non-string sequence
        Point = namedtuple('Point', ('x', 'y'))
        p = Point(x=11, y=22)
        self.assertEqual(repr(p), 'Point(x=11, y=22)')

    def test_tupleness(self):
        Point = namedtuple('Point', 'x y')
        p = Point(11, 22)

        self.assertIsInstance(p, tuple)
        self.assertEqual(p, (11, 22))                                       # matches a real tuple
        self.assertEqual(tuple(p), (11, 22))                                # coercible to a real tuple
        self.assertEqual(list(p), [11, 22])                                 # coercible to a list
        self.assertEqual(max(p), 22)                                        # iterable
        self.assertEqual(max(*p), 22)                                       # star-able
        x, y = p
        self.assertEqual(p, (x, y))                                         # unpacks like a tuple
        self.assertEqual((p[0], p[1]), (11, 22))                            # indexable like a tuple
        with self.assertRaises(IndexError):
            p[3]
        self.assertEqual(p[-1], 22)
        self.assertEqual(hash(p), hash((11, 22)))

        self.assertEqual(p.x, x)
        self.assertEqual(p.y, y)
        with self.assertRaises(AttributeError):
            p.z

    def test_odd_sizes(self):
        Zero = namedtuple('Zero', '')
        self.assertEqual(Zero(), ())
        self.assertEqual(Zero._make([]), ())
        self.assertEqual(repr(Zero()), 'Zero()')
        self.assertEqual(Zero()._asdict(), {})
        self.assertEqual(Zero()._fields, ())

        Dot = namedtuple('Dot', 'd')
        self.assertEqual(Dot(1), (1,))
        self.assertEqual(Dot._make([1]), (1,))
        self.assertEqual(Dot(1).d, 1)
        self.assertEqual(repr(Dot(1)), 'Dot(d=1)')
        self.assertEqual(Dot(1)._asdict(), {'d':1})
        self.assertEqual(Dot(1)._replace(d=999), (999,))
        self.assertEqual(Dot(1)._fields, ('d',))

    @support.requires_resource('cpu')
    def test_large_size(self):
        n = support.exceeds_recursion_limit()
        names = list(set(''.join([choice(string.ascii_letters)
                                  for j in range(10)]) for i in range(n)))
        n = len(names)
        Big = namedtuple('Big', names)
        b = Big(*range(n))
        self.assertEqual(b, tuple(range(n)))
        self.assertEqual(Big._make(range(n)), tuple(range(n)))
        for pos, name in enumerate(names):
            self.assertEqual(getattr(b, name), pos)
        repr(b)                                 # make sure repr() doesn't blow-up
        d = b._asdict()
        d_expected = dict(zip(names, range(n)))
        self.assertEqual(d, d_expected)
        b2 = b._replace(**dict([(names[1], 999),(names[-5], 42)]))
        b2_expected = list(range(n))
        b2_expected[1] = 999
        b2_expected[-5] = 42
        self.assertEqual(b2, tuple(b2_expected))
        self.assertEqual(b._fields, tuple(names))

    def test_pickle(self):
        p = TestNT(x=10, y=20, z=30)
        for module in (pickle,):
            loads = getattr(module, 'loads')
            dumps = getattr(module, 'dumps')
            for protocol in range(-1, module.HIGHEST_PROTOCOL + 1):
                q = loads(dumps(p, protocol))
                self.assertEqual(p, q)
                self.assertEqual(p._fields, q._fields)
                self.assertNotIn(b'OrderedDict', dumps(p, protocol))

    def test_copy(self):
        p = TestNT(x=10, y=20, z=30)
        for copier in copy.copy, copy.deepcopy:
            q = copier(p)
            self.assertEqual(p, q)
            self.assertEqual(p._fields, q._fields)

    def test_name_conflicts(self):
        # Some names like "self", "cls", "tuple", "itemgetter", and "property"
        # failed when used as field names.  Test to make sure these now work.
        T = namedtuple('T', 'itemgetter property self cls tuple')
        t = T(1, 2, 3, 4, 5)
        self.assertEqual(t, (1,2,3,4,5))
        newt = t._replace(itemgetter=10, property=20, self=30, cls=40, tuple=50)
        self.assertEqual(newt, (10,20,30,40,50))

       # Broader test of all interesting names taken from the code, old
       # template, and an example
        words = {'Alias', 'At', 'AttributeError', 'Build', 'Bypass', 'Create',
        'Encountered', 'Expected', 'Field', 'For', 'Got', 'Helper',
        'IronPython', 'Jython', 'KeyError', 'Make', 'Modify', 'Note',
        'OrderedDict', 'Point', 'Return', 'Returns', 'Type', 'TypeError',
        'Used', 'Validate', 'ValueError', 'Variables', 'a', 'accessible', 'add',
        'added', 'all', 'also', 'an', 'arg_list', 'args', 'arguments',
        'automatically', 'be', 'build', 'builtins', 'but', 'by', 'cannot',
        'class_namespace', 'classmethod', 'cls', 'collections', 'convert',
        'copy', 'created', 'creation', 'd', 'debugging', 'defined', 'dict',
        'dictionary', 'doc', 'docstring', 'docstrings', 'duplicate', 'effect',
        'either', 'enumerate', 'environments', 'error', 'example', 'exec', 'f',
        'f_globals', 'field', 'field_names', 'fields', 'formatted', 'frame',
        'function', 'functions', 'generate', 'get', 'getter', 'got', 'greater',
        'has', 'help', 'identifiers', 'index', 'indexable', 'instance',
        'instantiate', 'interning', 'introspection', 'isidentifier',
        'isinstance', 'itemgetter', 'iterable', 'join', 'keyword', 'keywords',
        'kwds', 'len', 'like', 'list', 'map', 'maps', 'message', 'metadata',
        'method', 'methods', 'module', 'module_name', 'must', 'name', 'named',
        'namedtuple', 'namedtuple_', 'names', 'namespace', 'needs', 'new',
        'nicely', 'num_fields', 'number', 'object', 'of', 'operator', 'option',
        'p', 'particular', 'pickle', 'pickling', 'plain', 'pop', 'positional',
        'property', 'r', 'regular', 'rename', 'replace', 'replacing', 'repr',
        'repr_fmt', 'representation', 'result', 'reuse_itemgetter', 's', 'seen',
        'self', 'sequence', 'set', 'side', 'specified', 'split', 'start',
        'startswith', 'step', 'str', 'string', 'strings', 'subclass', 'sys',
        'targets', 'than', 'the', 'their', 'this', 'to', 'tuple', 'tuple_new',
        'type', 'typename', 'underscore', 'unexpected', 'unpack', 'up', 'use',
        'used', 'user', 'valid', 'values', 'variable', 'verbose', 'where',
        'which', 'work', 'x', 'y', 'z', 'zip'}
        T = namedtuple('T', words)
        # test __new__
        values = tuple(range(len(words)))
        t = T(*values)
        self.assertEqual(t, values)
        t = T(**dict(zip(T._fields, values)))
        self.assertEqual(t, values)
        # test _make
        t = T._make(values)
        self.assertEqual(t, values)
        # exercise __repr__
        repr(t)
        # test _asdict
        self.assertEqual(t._asdict(), dict(zip(T._fields, values)))
        # test _replace
        t = T._make(values)
        newvalues = tuple(v*10 for v in values)
        newt = t._replace(**dict(zip(T._fields, newvalues)))
        self.assertEqual(newt, newvalues)
        # test _fields
        self.assertEqual(T._fields, tuple(words))
        # test __getnewargs__
        self.assertEqual(t.__getnewargs__(), values)

    def test_repr(self):
        A = namedtuple('A', 'x')
        self.assertEqual(repr(A(1)), 'A(x=1)')
        # repr should show the name of the subclass
        class B(A):
            pass
        self.assertEqual(repr(B(1)), 'B(x=1)')

    def test_keyword_only_arguments(self):
        # See issue 25628
        with self.assertRaises(TypeError):
            NT = namedtuple('NT', ['x', 'y'], True)

        NT = namedtuple('NT', ['abc', 'def'], rename=True)
        self.assertEqual(NT._fields, ('abc', '_1'))
        with self.assertRaises(TypeError):
            NT = namedtuple('NT', ['abc', 'def'], False, True)

    def test_namedtuple_subclass_issue_24931(self):
        class Point(namedtuple('_Point', ['x', 'y'])):
            pass

        a = Point(3, 4)
        self.assertEqual(a._asdict(), OrderedDict([('x', 3), ('y', 4)]))

        a.w = 5
        self.assertEqual(a.__dict__, {'w': 5})

    @support.cpython_only
    def test_field_descriptor(self):
        Point = namedtuple('Point', 'x y')
        p = Point(11, 22)
        self.assertTrue(inspect.isdatadescriptor(Point.x))
        self.assertEqual(Point.x.__get__(p), 11)
        self.assertRaises(AttributeError, Point.x.__set__, p, 33)
        self.assertRaises(AttributeError, Point.x.__delete__, p)

        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
            with self.subTest(proto=proto):
                class NewPoint(tuple):
                    x = pickle.loads(pickle.dumps(Point.x, proto))
                    y = pickle.loads(pickle.dumps(Point.y, proto))

                np = NewPoint([1, 2])

                self.assertEqual(np.x, 1)
                self.assertEqual(np.y, 2)

    def test_new_builtins_issue_43102(self):
        obj = namedtuple('C', ())
        new_func = obj.__new__
        self.assertEqual(new_func.__globals__['__builtins__'], {})
        self.assertEqual(new_func.__builtins__, {})

    def test_match_args(self):
        Point = namedtuple('Point', 'x y')
        self.assertEqual(Point.__match_args__, ('x', 'y'))

    def test_non_generic_subscript(self):
        # For backward compatibility, subscription works
        # on arbitrary named tuple types.
        Group = collections.namedtuple('Group', 'key group')
        A = Group[int, list[int]]
        self.assertEqual(A.__origin__, Group)
        self.assertEqual(A.__parameters__, ())
        self.assertEqual(A.__args__, (int, list[int]))
        a = A(1, [2])
        self.assertIs(type(a), Group)
        self.assertEqual(a, (1, [2]))


################################################################################
### Abstract Base Classes
################################################################################

class ABCTestCase(unittest.TestCase):

    def validate_abstract_methods(self, abc, *names):
        methodstubs = dict.fromkeys(names, lambda s, *args: 0)

        # everything should work will all required methods are present
        C = type('C', (abc,), methodstubs)
        C()

        # instantiation should fail if a required method is missing
        for name in names:
            stubs = methodstubs.copy()
            del stubs[name]
            C = type('C', (abc,), stubs)
            self.assertRaises(TypeError, C)

    def validate_isinstance(self, abc, name):
        stub = lambda s, *args: 0

        C = type('C', (object,), {'__hash__': None})
        setattr(C, name, stub)
        self.assertIsInstance(C(), abc)
        self.assertIsSubclass(C, abc)

        C = type('C', (object,), {'__hash__': None})
        self.assertNotIsInstance(C(), abc)
        self.assertNotIsSubclass(C, abc)

    def validate_comparison(self, instance):
        ops = ['lt', 'gt', 'le', 'ge', 'ne', 'or', 'and', 'xor', 'sub']
        operators = {}
        for op in ops:
            name = '__' + op + '__'
            operators[name] = getattr(operator, name)

        class Other:
            def __init__(self):
                self.right_side = False
            def __eq__(self, other):
                self.right_side = True
                return True
            __lt__ = __eq__
            __gt__ = __eq__
            __le__ = __eq__
            __ge__ = __eq__
            __ne__ = __eq__
            __ror__ = __eq__
            __rand__ = __eq__
            __rxor__ = __eq__
            __rsub__ = __eq__

        for name, op in operators.items():
            if not hasattr(instance, name):
                continue
            other = Other()
            op(instance, other)
            self.assertTrue(other.right_side,'Right side not called for %s.%s'
                            % (type(instance), name))

def _test_gen():
    yield

class TestOneTrickPonyABCs(ABCTestCase):

    def test_Awaitable(self):
        def gen():
            yield

        @types.coroutine
        def coro():
            yield

        async def new_coro():
            pass

        class Bar:
            def __await__(self):
                yield

        class MinimalCoro(Coroutine):
            def send(self, value):
                return value
            def throw(self, typ, val=None, tb=None):
                super().throw(typ, val, tb)
            def __await__(self):
                yield

        self.validate_abstract_methods(Awaitable, '__await__')

        non_samples = [None, int(), gen(), object()]
        for x in non_samples:
            self.assertNotIsInstance(x, Awaitable)
            self.assertNotIsSubclass(type(x), Awaitable)

        samples = [Bar(), MinimalCoro()]
        for x in samples:
            self.assertIsInstance(x, Awaitable)
            self.assertIsSubclass(type(x), Awaitable)

        c = coro()
        # Iterable coroutines (generators with CO_ITERABLE_COROUTINE
        # flag don't have '__await__' method, hence can't be instances
        # of Awaitable. Use inspect.isawaitable to detect them.
        self.assertNotIsInstance(c, Awaitable)

        c = new_coro()
        self.assertIsInstance(c, Awaitable)
        c.close() # avoid RuntimeWarning that coro() was not awaited

        class CoroLike: pass
        Coroutine.register(CoroLike)
        self.assertIsInstance(CoroLike(), Awaitable)
        self.assertIsSubclass(CoroLike, Awaitable)
        CoroLike = None
        support.gc_collect() # Kill CoroLike to clean-up ABCMeta cache

    def test_Coroutine(self):
        def gen():
            yield

        @types.coroutine
        def coro():
            yield

        async def new_coro():
            pass

        class Bar:
            def __await__(self):
                yield

        class MinimalCoro(Coroutine):
            def send(self, value):
                return value
            def throw(self, typ, val=None, tb=None):
                super().throw(typ, val, tb)
            def __await__(self):
                yield

        self.validate_abstract_methods(Coroutine, '__await__', 'send', 'throw')

        non_samples = [None, int(), gen(), object(), Bar()]
        for x in non_samples:
            self.assertNotIsInstance(x, Coroutine)
            self.assertNotIsSubclass(type(x), Coroutine)

        samples = [MinimalCoro()]
        for x in samples:
            self.assertIsInstance(x, Awaitable)
            self.assertIsSubclass(type(x), Awaitable)

        c = coro()
        # Iterable coroutines (generators with CO_ITERABLE_COROUTINE
        # flag don't have '__await__' method, hence can't be instances
        # of Coroutine. Use inspect.isawaitable to detect them.
        self.assertNotIsInstance(c, Coroutine)

        c = new_coro()
        self.assertIsInstance(c, Coroutine)
        c.close() # avoid RuntimeWarning that coro() was not awaited

        class CoroLike:
            def send(self, value):
                pass
            def throw(self, typ, val=None, tb=None):
                pass
            def close(self):
                pass
            def __await__(self):
                pass
        self.assertIsInstance(CoroLike(), Coroutine)
        self.assertIsSubclass(CoroLike, Coroutine)

        class CoroLike:
            def send(self, value):
                pass
            def close(self):
                pass
            def __await__(self):
                pass
        self.assertNotIsInstance(CoroLike(), Coroutine)
        self.assertNotIsSubclass(CoroLike, Coroutine)

    def test_Hashable(self):
        # Check some non-hashables
        non_samples = [bytearray(), list(), set(), dict()]
        for x in non_samples:
            self.assertNotIsInstance(x, Hashable)
            self.assertNotIsSubclass(type(x), Hashable)
        # Check some hashables
        samples = [None,
                   int(), float(), complex(),
                   str(),
                   tuple(), frozenset(),
                   int, list, object, type, bytes()
                   ]
        for x in samples:
            self.assertIsInstance(x, Hashable)
            self.assertIsSubclass(type(x), Hashable)
        self.assertRaises(TypeError, Hashable)
        # Check direct subclassing
        class H(Hashable):
            def __hash__(self):
                return super().__hash__()
        self.assertEqual(hash(H()), 0)
        self.assertNotIsSubclass(int, H)
        self.validate_abstract_methods(Hashable, '__hash__')
        self.validate_isinstance(Hashable, '__hash__')

    def test_AsyncIterable(self):
        class AI:
            def __aiter__(self):
                return self
        self.assertIsInstance(AI(), AsyncIterable)
        self.assertIsSubclass(AI, AsyncIterable)
        # Check some non-iterables
        non_samples = [None, object, []]
        for x in non_samples:
            self.assertNotIsInstance(x, AsyncIterable)
            self.assertNotIsSubclass(type(x), AsyncIterable)
        self.validate_abstract_methods(AsyncIterable, '__aiter__')
        self.validate_isinstance(AsyncIterable, '__aiter__')

    def test_AsyncIterator(self):
        class AI:
            def __aiter__(self):
                return self
            async def __anext__(self):
                raise StopAsyncIteration
        self.assertIsInstance(AI(), AsyncIterator)
        self.assertIsSubclass(AI, AsyncIterator)
        non_samples = [None, object, []]
        # Check some non-iterables
        for x in non_samples:
            self.assertNotIsInstance(x, AsyncIterator)
            self.assertNotIsSubclass(type(x), AsyncIterator)
        # Similarly to regular iterators (see issue 10565)
        class AnextOnly:
            async def __anext__(self):
                raise StopAsyncIteration
        self.assertNotIsInstance(AnextOnly(), AsyncIterator)
        self.validate_abstract_methods(AsyncIterator, '__anext__')

    def test_Iterable(self):
        # Check some non-iterables
        non_samples = [None, 42, 3.14, 1j]
        for x in non_samples:
            self.assertNotIsInstance(x, Iterable)
            self.assertNotIsSubclass(type(x), Iterable)
        # Check some iterables
        samples = [bytes(), str(),
                   tuple(), list(), set(), frozenset(), dict(),
                   dict().keys(), dict().items(), dict().values(),
                   _test_gen(),
                   (x for x in []),
                   ]
        for x in samples:
            self.assertIsInstance(x, Iterable)
            self.assertIsSubclass(type(x), Iterable)
        # Check direct subclassing
        class I(Iterable):
            def __iter__(self):
                return super().__iter__()
        self.assertEqual(list(I()), [])
        self.assertNotIsSubclass(str, I)
        self.validate_abstract_methods(Iterable, '__iter__')
        self.validate_isinstance(Iterable, '__iter__')
        # Check None blocking
        class It:
            def __iter__(self): return iter([])
        class ItBlocked(It):
            __iter__ = None
        self.assertIsSubclass(It, Iterable)
        self.assertIsInstance(It(), Iterable)
        self.assertNotIsSubclass(ItBlocked, Iterable)
        self.assertNotIsInstance(ItBlocked(), Iterable)

    def test_Reversible(self):
        # Check some non-reversibles
        non_samples = [None, 42, 3.14, 1j, set(), frozenset()]
        for x in non_samples:
            self.assertNotIsInstance(x, Reversible)
            self.assertNotIsSubclass(type(x), Reversible)
        # Check some non-reversible iterables
        non_reversibles = [_test_gen(), (x for x in []), iter([]), reversed([])]
        for x in non_reversibles:
            self.assertNotIsInstance(x, Reversible)
            self.assertNotIsSubclass(type(x), Reversible)
        # Check some reversible iterables
        samples = [bytes(), str(), tuple(), list(), OrderedDict(),
                   OrderedDict().keys(), OrderedDict().items(),
                   OrderedDict().values(), Counter(), Counter().keys(),
                   Counter().items(), Counter().values(), dict(),
                   dict().keys(), dict().items(), dict().values()]
        for x in samples:
            self.assertIsInstance(x, Reversible)
            self.assertIsSubclass(type(x), Reversible)
        # Check also Mapping, MutableMapping, and Sequence
        self.assertIsSubclass(Sequence, Reversible)
        self.assertNotIsSubclass(Mapping, Reversible)
        self.assertNotIsSubclass(MutableMapping, Reversible)
        # Check direct subclassing
        class R(Reversible):
            def __iter__(self):
                return iter(list())
            def __reversed__(self):
                return iter(list())
        self.assertEqual(list(reversed(R())), [])
        self.assertNotIsSubclass(float, R)
        self.validate_abstract_methods(Reversible, '__reversed__', '__iter__')
        # Check reversible non-iterable (which is not Reversible)
        class RevNoIter:
            def __reversed__(self): return reversed([])
        class RevPlusIter(RevNoIter):
            def __iter__(self): return iter([])
        self.assertNotIsSubclass(RevNoIter, Reversible)
        self.assertNotIsInstance(RevNoIter(), Reversible)
        self.assertIsSubclass(RevPlusIter, Reversible)
        self.assertIsInstance(RevPlusIter(), Reversible)
        # Check None blocking
        class Rev:
            def __iter__(self): return iter([])
            def __reversed__(self): return reversed([])
        class RevItBlocked(Rev):
            __iter__ = None
        class RevRevBlocked(Rev):
            __reversed__ = None
        self.assertIsSubclass(Rev, Reversible)
        self.assertIsInstance(Rev(), Reversible)
        self.assertNotIsSubclass(RevItBlocked, Reversible)
        self.assertNotIsInstance(RevItBlocked(), Reversible)
        self.assertNotIsSubclass(RevRevBlocked, Reversible)
        self.assertNotIsInstance(RevRevBlocked(), Reversible)

    def test_Collection(self):
        # Check some non-collections
        non_collections = [None, 42, 3.14, 1j, lambda x: 2*x]
        for x in non_collections:
            self.assertNotIsInstance(x, Collection)
            self.assertNotIsSubclass(type(x), Collection)
        # Check some non-collection iterables
        non_col_iterables = [_test_gen(), iter(b''), iter(bytearray()),
                             (x for x in [])]
        for x in non_col_iterables:
            self.assertNotIsInstance(x, Collection)
            self.assertNotIsSubclass(type(x), Collection)
        # Check some collections
        samples = [set(), frozenset(), dict(), bytes(), str(), tuple(),
                   list(), dict().keys(), dict().items(), dict().values()]
        for x in samples:
            self.assertIsInstance(x, Collection)
            self.assertIsSubclass(type(x), Collection)
        # Check also Mapping, MutableMapping, etc.
        self.assertIsSubclass(Sequence, Collection)
        self.assertIsSubclass(Mapping, Collection)
        self.assertIsSubclass(MutableMapping, Collection)
        self.assertIsSubclass(Set, Collection)
        self.assertIsSubclass(MutableSet, Collection)
        self.assertIsSubclass(Sequence, Collection)
        # Check direct subclassing
        class Col(Collection):
            def __iter__(self):
                return iter(list())
            def __len__(self):
                return 0
            def __contains__(self, item):
                return False
        class DerCol(Col): pass
        self.assertEqual(list(iter(Col())), [])
        self.assertNotIsSubclass(list, Col)
        self.assertNotIsSubclass(set, Col)
        self.assertNotIsSubclass(float, Col)
        self.assertEqual(list(iter(DerCol())), [])
        self.assertNotIsSubclass(list, DerCol)
        self.assertNotIsSubclass(set, DerCol)
        self.assertNotIsSubclass(float, DerCol)
        self.validate_abstract_methods(Collection, '__len__', '__iter__',
                                                   '__contains__')
        # Check sized container non-iterable (which is not Collection) etc.
        class ColNoIter:
            def __len__(self): return 0
            def __contains__(self, item): return False
        class ColNoSize:
            def __iter__(self): return iter([])
            def __contains__(self, item): return False
        class ColNoCont:
            def __iter__(self): return iter([])
            def __len__(self): return 0
        self.assertNotIsSubclass(ColNoIter, Collection)
        self.assertNotIsInstance(ColNoIter(), Collection)
        self.assertNotIsSubclass(ColNoSize, Collection)
        self.assertNotIsInstance(ColNoSize(), Collection)
        self.assertNotIsSubclass(ColNoCont, Collection)
        self.assertNotIsInstance(ColNoCont(), Collection)
        # Check None blocking
        class SizeBlock:
            def __iter__(self): return iter([])
            def __contains__(self): return False
            __len__ = None
        class IterBlock:
            def __len__(self): return 0
            def __contains__(self): return True
            __iter__ = None
        self.assertNotIsSubclass(SizeBlock, Collection)
        self.assertNotIsInstance(SizeBlock(), Collection)
        self.assertNotIsSubclass(IterBlock, Collection)
        self.assertNotIsInstance(IterBlock(), Collection)
        # Check None blocking in subclass
        class ColImpl:
            def __iter__(self):
                return iter(list())
            def __len__(self):
                return 0
            def __contains__(self, item):
                return False
        class NonCol(ColImpl):
            __contains__ = None
        self.assertNotIsSubclass(NonCol, Collection)
        self.assertNotIsInstance(NonCol(), Collection)


    def test_Iterator(self):
        non_samples = [None, 42, 3.14, 1j, b"", "", (), [], {}, set()]
        for x in non_samples:
            self.assertNotIsInstance(x, Iterator)
            self.assertNotIsSubclass(type(x), Iterator)
        samples = [iter(bytes()), iter(str()),
                   iter(tuple()), iter(list()), iter(dict()),
                   iter(set()), iter(frozenset()),
                   iter(dict().keys()), iter(dict().items()),
                   iter(dict().values()),
                   _test_gen(),
                   (x for x in []),
                   ]
        for x in samples:
            self.assertIsInstance(x, Iterator)
            self.assertIsSubclass(type(x), Iterator)
        self.validate_abstract_methods(Iterator, '__next__')

        # Issue 10565
        class NextOnly:
            def __next__(self):
                yield 1
                return
        self.assertNotIsInstance(NextOnly(), Iterator)

    def test_Generator(self):
        class NonGen1:
            def __iter__(self): return self
            def __next__(self): return None
            def close(self): pass
            def throw(self, typ, val=None, tb=None): pass

        class NonGen2:
            def __iter__(self): return self
            def __next__(self): return None
            def close(self): pass
            def send(self, value): return value

        class NonGen3:
            def close(self): pass
            def send(self, value): return value
            def throw(self, typ, val=None, tb=None): pass

        non_samples = [
            None, 42, 3.14, 1j, b"", "", (), [], {}, set(),
            iter(()), iter([]), NonGen1(), NonGen2(), NonGen3()]
        for x in non_samples:
            self.assertNotIsInstance(x, Generator)
            self.assertNotIsSubclass(type(x), Generator)

        class Gen:
            def __iter__(self): return self
            def __next__(self): return None
            def close(self): pass
            def send(self, value): return value
            def throw(self, typ, val=None, tb=None): pass

        class MinimalGen(Generator):
            def send(self, value):
                return value
            def throw(self, typ, val=None, tb=None):
                super().throw(typ, val, tb)

        def gen():
            yield 1

        samples = [gen(), (lambda: (yield))(), Gen(), MinimalGen()]
        for x in samples:
            self.assertIsInstance(x, Iterator)
            self.assertIsInstance(x, Generator)
            self.assertIsSubclass(type(x), Generator)
        self.validate_abstract_methods(Generator, 'send', 'throw')

        # mixin tests
        mgen = MinimalGen()
        self.assertIs(mgen, iter(mgen))
        self.assertIs(mgen.send(None), next(mgen))
        self.assertEqual(2, mgen.send(2))
        self.assertIsNone(mgen.close())
        self.assertRaises(ValueError, mgen.throw, ValueError)
        self.assertRaisesRegex(ValueError, "^huhu$",
                               mgen.throw, ValueError, ValueError("huhu"))
        self.assertRaises(StopIteration, mgen.throw, StopIteration())

        class FailOnClose(Generator):
            def send(self, value): return value
            def throw(self, *args): raise ValueError

        self.assertRaises(ValueError, FailOnClose().close)

        class IgnoreGeneratorExit(Generator):
            def send(self, value): return value
            def throw(self, *args): pass

        self.assertRaises(RuntimeError, IgnoreGeneratorExit().close)

    def test_AsyncGenerator(self):
        class NonAGen1:
            def __aiter__(self): return self
            def __anext__(self): return None
            def aclose(self): pass
            def athrow(self, typ, val=None, tb=None): pass

        class NonAGen2:
            def __aiter__(self): return self
            def __anext__(self): return None
            def aclose(self): pass
            def asend(self, value): return value

        class NonAGen3:
            def aclose(self): pass
            def asend(self, value): return value
            def athrow(self, typ, val=None, tb=None): pass

        non_samples = [
            None, 42, 3.14, 1j, b"", "", (), [], {}, set(),
            iter(()), iter([]), NonAGen1(), NonAGen2(), NonAGen3()]
        for x in non_samples:
            self.assertNotIsInstance(x, AsyncGenerator)
            self.assertNotIsSubclass(type(x), AsyncGenerator)

        class Gen:
            def __aiter__(self): return self
            async def __anext__(self): return None
            async def aclose(self): pass
            async def asend(self, value): return value
            async def athrow(self, typ, val=None, tb=None): pass

        class MinimalAGen(AsyncGenerator):
            async def asend(self, value):
                return value
            async def athrow(self, typ, val=None, tb=None):
                await super().athrow(typ, val, tb)

        async def gen():
            yield 1

        samples = [gen(), Gen(), MinimalAGen()]
        for x in samples:
            self.assertIsInstance(x, AsyncIterator)
            self.assertIsInstance(x, AsyncGenerator)
            self.assertIsSubclass(type(x), AsyncGenerator)
        self.validate_abstract_methods(AsyncGenerator, 'asend', 'athrow')

        def run_async(coro):
            result = None
            while True:
                try:
                    coro.send(None)
                except StopIteration as ex:
                    result = ex.args[0] if ex.args else None
                    break
            return result

        # mixin tests
        mgen = MinimalAGen()
        self.assertIs(mgen, mgen.__aiter__())
        self.assertIs(run_async(mgen.asend(None)), run_async(mgen.__anext__()))
        self.assertEqual(2, run_async(mgen.asend(2)))
        self.assertIsNone(run_async(mgen.aclose()))
        with self.assertRaises(ValueError):
            run_async(mgen.athrow(ValueError))

        class FailOnClose(AsyncGenerator):
            async def asend(self, value): return value
            async def athrow(self, *args): raise ValueError

        with self.assertRaises(ValueError):
            run_async(FailOnClose().aclose())

        class IgnoreGeneratorExit(AsyncGenerator):
            async def asend(self, value): return value
            async def athrow(self, *args): pass

        with self.assertRaises(RuntimeError):
            run_async(IgnoreGeneratorExit().aclose())

    def test_Sized(self):
        non_samples = [None, 42, 3.14, 1j,
                       _test_gen(),
                       (x for x in []),
                       ]
        for x in non_samples:
            self.assertNotIsInstance(x, Sized)
            self.assertNotIsSubclass(type(x), Sized)
        samples = [bytes(), str(),
                   tuple(), list(), set(), frozenset(), dict(),
                   dict().keys(), dict().items(), dict().values(),
                   ]
        for x in samples:
            self.assertIsInstance(x, Sized)
            self.assertIsSubclass(type(x), Sized)
        self.validate_abstract_methods(Sized, '__len__')
        self.validate_isinstance(Sized, '__len__')

    def test_Container(self):
        non_samples = [None, 42, 3.14, 1j,
                       _test_gen(),
                       (x for x in []),
                       ]
        for x in non_samples:
            self.assertNotIsInstance(x, Container)
            self.assertNotIsSubclass(type(x), Container)
        samples = [bytes(), str(),
                   tuple(), list(), set(), frozenset(), dict(),
                   dict().keys(), dict().items(),
                   ]
        for x in samples:
            self.assertIsInstance(x, Container)
            self.assertIsSubclass(type(x), Container)
        self.validate_abstract_methods(Container, '__contains__')
        self.validate_isinstance(Container, '__contains__')

    def test_Callable(self):
        non_samples = [None, 42, 3.14, 1j,
                       "", b"", (), [], {}, set(),
                       _test_gen(),
                       (x for x in []),
                       ]
        for x in non_samples:
            self.assertNotIsInstance(x, Callable)
            self.assertNotIsSubclass(type(x), Callable)
        samples = [lambda: None,
                   type, int, object,
                   len,
                   list.append, [].append,
                   ]
        for x in samples:
            self.assertIsInstance(x, Callable)
            self.assertIsSubclass(type(x), Callable)
        self.validate_abstract_methods(Callable, '__call__')
        self.validate_isinstance(Callable, '__call__')

    def test_direct_subclassing(self):
        for B in Hashable, Iterable, Iterator, Reversible, Sized, Container, Callable:
            class C(B):
                pass
            self.assertIsSubclass(C, B)
            self.assertNotIsSubclass(int, C)

    def test_registration(self):
        for B in Hashable, Iterable, Iterator, Reversible, Sized, Container, Callable:
            class C:
                __hash__ = None  # Make sure it isn't hashable by default
            self.assertNotIsSubclass(C, B)
            B.register(C)
            self.assertIsSubclass(C, B)

class WithSet(MutableSet):

    def __init__(self, it=()):
        self.data = set(it)

    def __len__(self):
        return len(self.data)

    def __iter__(self):
        return iter(self.data)

    def __contains__(self, item):
        return item in self.data

    def add(self, item):
        self.data.add(item)

    def discard(self, item):
        self.data.discard(item)

class TestCollectionABCs(ABCTestCase):

    # XXX For now, we only test some virtual inheritance properties.
    # We should also test the proper behavior of the collection ABCs
    # as real base classes or mix-in classes.

    def test_Set(self):
        for sample in [set, frozenset]:
            self.assertIsInstance(sample(), Set)
            self.assertIsSubclass(sample, Set)
        self.validate_abstract_methods(Set, '__contains__', '__iter__', '__len__')
        class MySet(Set):
            def __contains__(self, x):
                return False
            def __len__(self):
                return 0
            def __iter__(self):
                return iter([])
        self.validate_comparison(MySet())

    def test_hash_Set(self):
        class OneTwoThreeSet(Set):
            def __init__(self):
                self.contents = [1, 2, 3]
            def __contains__(self, x):
                return x in self.contents
            def __len__(self):
                return len(self.contents)
            def __iter__(self):
                return iter(self.contents)
            def __hash__(self):
                return self._hash()
        a, b = OneTwoThreeSet(), OneTwoThreeSet()
        self.assertTrue(hash(a) == hash(b))

    def test_isdisjoint_Set(self):
        class MySet(Set):
            def __init__(self, itr):
                self.contents = itr
            def __contains__(self, x):
                return x in self.contents
            def __iter__(self):
                return iter(self.contents)
            def __len__(self):
                return len([x for x in self.contents])
        s1 = MySet((1, 2, 3))
        s2 = MySet((4, 5, 6))
        s3 = MySet((1, 5, 6))
        self.assertTrue(s1.isdisjoint(s2))
        self.assertFalse(s1.isdisjoint(s3))

    def test_equality_Set(self):
        class MySet(Set):
            def __init__(self, itr):
                self.contents = itr
            def __contains__(self, x):
                return x in self.contents
            def __iter__(self):
                return iter(self.contents)
            def __len__(self):
                return len([x for x in self.contents])
        s1 = MySet((1,))
        s2 = MySet((1, 2))
        s3 = MySet((3, 4))
        s4 = MySet((3, 4))
        self.assertTrue(s2 > s1)
        self.assertTrue(s1 < s2)
        self.assertFalse(s2 <= s1)
        self.assertFalse(s2 <= s3)
        self.assertFalse(s1 >= s2)
        self.assertEqual(s3, s4)
        self.assertNotEqual(s2, s3)

    def test_arithmetic_Set(self):
        class MySet(Set):
            def __init__(self, itr):
                self.contents = itr
            def __contains__(self, x):
                return x in self.contents
            def __iter__(self):
                return iter(self.contents)
            def __len__(self):
                return len([x for x in self.contents])
        s1 = MySet((1, 2, 3))
        s2 = MySet((3, 4, 5))
        s3 = s1 & s2
        self.assertEqual(s3, MySet((3,)))

    def test_MutableSet(self):
        self.assertIsInstance(set(), MutableSet)
        self.assertIsSubclass(set, MutableSet)
        self.assertNotIsInstance(frozenset(), MutableSet)
        self.assertNotIsSubclass(frozenset, MutableSet)
        self.validate_abstract_methods(MutableSet, '__contains__', '__iter__', '__len__',
            'add', 'discard')

    def test_issue_5647(self):
        # MutableSet.__iand__ mutated the set during iteration
        s = WithSet('abcd')
        s &= WithSet('cdef')            # This used to fail
        self.assertEqual(set(s), set('cd'))

    def test_issue_4920(self):
        # MutableSet.pop() method did not work
        class MySet(MutableSet):
            __slots__=['__s']
            def __init__(self,items=None):
                if items is None:
                    items=[]
                self.__s=set(items)
            def __contains__(self,v):
                return v in self.__s
            def __iter__(self):
                return iter(self.__s)
            def __len__(self):
                return len(self.__s)
            def add(self,v):
                result=v not in self.__s
                self.__s.add(v)
                return result
            def discard(self,v):
                result=v in self.__s
                self.__s.discard(v)
                return result
            def __repr__(self):
                return "MySet(%s)" % repr(list(self))
        items = [5,43,2,1]
        s = MySet(items)
        r = s.pop()
        self.assertEqual(len(s), len(items) - 1)
        self.assertNotIn(r, s)
        self.assertIn(r, items)

    def test_issue8750(self):
        empty = WithSet()
        full = WithSet(range(10))
        s = WithSet(full)
        s -= s
        self.assertEqual(s, empty)
        s = WithSet(full)
        s ^= s
        self.assertEqual(s, empty)
        s = WithSet(full)
        s &= s
        self.assertEqual(s, full)
        s |= s
        self.assertEqual(s, full)

    def test_issue16373(self):
        # Recursion error comparing comparable and noncomparable
        # Set instances
        class MyComparableSet(Set):
            def __contains__(self, x):
                return False
            def __len__(self):
                return 0
            def __iter__(self):
                return iter([])
        class MyNonComparableSet(Set):
            def __contains__(self, x):
                return False
            def __len__(self):
                return 0
            def __iter__(self):
                return iter([])
            def __le__(self, x):
                return NotImplemented
            def __lt__(self, x):
                return NotImplemented

        cs = MyComparableSet()
        ncs = MyNonComparableSet()
        self.assertFalse(ncs < cs)
        self.assertTrue(ncs <= cs)
        self.assertFalse(ncs > cs)
        self.assertTrue(ncs >= cs)

    def test_issue26915(self):
        # Container membership test should check identity first
        class CustomSequence(Sequence):
            def __init__(self, seq):
                self._seq = seq
            def __getitem__(self, index):
                return self._seq[index]
            def __len__(self):
                return len(self._seq)

        nan = float('nan')
        obj = support.NEVER_EQ
        seq = CustomSequence([nan, obj, nan])
        containers = [
            seq,
            ItemsView({1: nan, 2: obj}),
            KeysView({1: nan, 2: obj}),
            ValuesView({1: nan, 2: obj})
        ]
        for container in containers:
            for elem in container:
                self.assertIn(elem, container)
        self.assertEqual(seq.index(nan), 0)
        self.assertEqual(seq.index(obj), 1)
        self.assertEqual(seq.count(nan), 2)
        self.assertEqual(seq.count(obj), 1)

    def assertSameSet(self, s1, s2):
        # coerce both to a real set then check equality
        self.assertSetEqual(set(s1), set(s2))

    def test_Set_from_iterable(self):
        """Verify _from_iterable overridden to an instance method works."""
        class SetUsingInstanceFromIterable(MutableSet):
            def __init__(self, values, created_by):
                if not created_by:
                    raise ValueError('created_by must be specified')
                self.created_by = created_by
                self._values = set(values)

            def _from_iterable(self, values):
                return type(self)(values, 'from_iterable')

            def __contains__(self, value):
                return value in self._values

            def __iter__(self):
                yield from self._values

            def __len__(self):
                return len(self._values)

            def add(self, value):
                self._values.add(value)

            def discard(self, value):
                self._values.discard(value)

        impl = SetUsingInstanceFromIterable([1, 2, 3], 'test')

        actual = impl - {1}
        self.assertIsInstance(actual, SetUsingInstanceFromIterable)
        self.assertEqual('from_iterable', actual.created_by)
        self.assertEqual({2, 3}, actual)

        actual = impl | {4}
        self.assertIsInstance(actual, SetUsingInstanceFromIterable)
        self.assertEqual('from_iterable', actual.created_by)
        self.assertEqual({1, 2, 3, 4}, actual)

        actual = impl & {2}
        self.assertIsInstance(actual, SetUsingInstanceFromIterable)
        self.assertEqual('from_iterable', actual.created_by)
        self.assertEqual({2}, actual)

        actual = impl ^ {3, 4}
        self.assertIsInstance(actual, SetUsingInstanceFromIterable)
        self.assertEqual('from_iterable', actual.created_by)
        self.assertEqual({1, 2, 4}, actual)

        # NOTE: ixor'ing with a list is important here: internally, __ixor__
        # only calls _from_iterable if the other value isn't already a Set.
        impl ^= [3, 4]
        self.assertIsInstance(impl, SetUsingInstanceFromIterable)
        self.assertEqual('test', impl.created_by)
        self.assertEqual({1, 2, 4}, impl)

    def test_Set_interoperability_with_real_sets(self):
        # Issue: 8743
        class ListSet(Set):
            def __init__(self, elements=()):
                self.data = []
                for elem in elements:
                    if elem not in self.data:
                        self.data.append(elem)
            def __contains__(self, elem):
                return elem in self.data
            def __iter__(self):
                return iter(self.data)
            def __len__(self):
                return len(self.data)
            def __repr__(self):
                return 'Set({!r})'.format(self.data)

        r1 = set('abc')
        r2 = set('bcd')
        r3 = set('abcde')
        f1 = ListSet('abc')
        f2 = ListSet('bcd')
        f3 = ListSet('abcde')
        l1 = list('abccba')
        l2 = list('bcddcb')
        l3 = list('abcdeedcba')

        target = r1 & r2
        self.assertSameSet(f1 & f2, target)
        self.assertSameSet(f1 & r2, target)
        self.assertSameSet(r2 & f1, target)
        self.assertSameSet(f1 & l2, target)

        target = r1 | r2
        self.assertSameSet(f1 | f2, target)
        self.assertSameSet(f1 | r2, target)
        self.assertSameSet(r2 | f1, target)
        self.assertSameSet(f1 | l2, target)

        fwd_target = r1 - r2
        rev_target = r2 - r1
        self.assertSameSet(f1 - f2, fwd_target)
        self.assertSameSet(f2 - f1, rev_target)
        self.assertSameSet(f1 - r2, fwd_target)
        self.assertSameSet(f2 - r1, rev_target)
        self.assertSameSet(r1 - f2, fwd_target)
        self.assertSameSet(r2 - f1, rev_target)
        self.assertSameSet(f1 - l2, fwd_target)
        self.assertSameSet(f2 - l1, rev_target)

        target = r1 ^ r2
        self.assertSameSet(f1 ^ f2, target)
        self.assertSameSet(f1 ^ r2, target)
        self.assertSameSet(r2 ^ f1, target)
        self.assertSameSet(f1 ^ l2, target)

        # Don't change the following to use assertLess or other
        # "more specific" unittest assertions.  The current
        # assertTrue/assertFalse style makes the pattern of test
        # case combinations clear and allows us to know for sure
        # the exact operator being invoked.

        # proper subset
        self.assertTrue(f1 < f3)
        self.assertFalse(f1 < f1)
        self.assertFalse(f1 < f2)
        self.assertTrue(r1 < f3)
        self.assertFalse(r1 < f1)
        self.assertFalse(r1 < f2)
        self.assertTrue(r1 < r3)
        self.assertFalse(r1 < r1)
        self.assertFalse(r1 < r2)
        with self.assertRaises(TypeError):
            f1 < l3
        with self.assertRaises(TypeError):
            f1 < l1
        with self.assertRaises(TypeError):
            f1 < l2

        # any subset
        self.assertTrue(f1 <= f3)
        self.assertTrue(f1 <= f1)
        self.assertFalse(f1 <= f2)
        self.assertTrue(r1 <= f3)
        self.assertTrue(r1 <= f1)
        self.assertFalse(r1 <= f2)
        self.assertTrue(r1 <= r3)
        self.assertTrue(r1 <= r1)
        self.assertFalse(r1 <= r2)
        with self.assertRaises(TypeError):
            f1 <= l3
        with self.assertRaises(TypeError):
            f1 <= l1
        with self.assertRaises(TypeError):
            f1 <= l2

        # proper superset
        self.assertTrue(f3 > f1)
        self.assertFalse(f1 > f1)
        self.assertFalse(f2 > f1)
        self.assertTrue(r3 > r1)
        self.assertFalse(f1 > r1)
        self.assertFalse(f2 > r1)
        self.assertTrue(r3 > r1)
        self.assertFalse(r1 > r1)
        self.assertFalse(r2 > r1)
        with self.assertRaises(TypeError):
            f1 > l3
        with self.assertRaises(TypeError):
            f1 > l1
        with self.assertRaises(TypeError):
            f1 > l2

        # any superset
        self.assertTrue(f3 >= f1)
        self.assertTrue(f1 >= f1)
        self.assertFalse(f2 >= f1)
        self.assertTrue(r3 >= r1)
        self.assertTrue(f1 >= r1)
        self.assertFalse(f2 >= r1)
        self.assertTrue(r3 >= r1)
        self.assertTrue(r1 >= r1)
        self.assertFalse(r2 >= r1)
        with self.assertRaises(TypeError):
            f1 >= l3
        with self.assertRaises(TypeError):
            f1 >=l1
        with self.assertRaises(TypeError):
            f1 >= l2

        # equality
        self.assertTrue(f1 == f1)
        self.assertTrue(r1 == f1)
        self.assertTrue(f1 == r1)
        self.assertFalse(f1 == f3)
        self.assertFalse(r1 == f3)
        self.assertFalse(f1 == r3)
        self.assertFalse(f1 == l3)
        self.assertFalse(f1 == l1)
        self.assertFalse(f1 == l2)

        # inequality
        self.assertFalse(f1 != f1)
        self.assertFalse(r1 != f1)
        self.assertFalse(f1 != r1)
        self.assertTrue(f1 != f3)
        self.assertTrue(r1 != f3)
        self.assertTrue(f1 != r3)
        self.assertTrue(f1 != l3)
        self.assertTrue(f1 != l1)
        self.assertTrue(f1 != l2)

    def test_Set_hash_matches_frozenset(self):
        sets = [
            {}, {1}, {None}, {-1}, {0.0}, {"abc"}, {1, 2, 3},
            {10**100, 10**101}, {"a", "b", "ab", ""}, {False, True},
            {object(), object(), object()}, {float("nan")},  {frozenset()},
            {*range(1000)}, {*range(1000)} - {100, 200, 300},
            {*range(sys.maxsize - 10, sys.maxsize + 10)},
        ]
        for s in sets:
            fs = frozenset(s)
            self.assertEqual(hash(fs), Set._hash(fs), msg=s)

    def test_Mapping(self):
        for sample in [dict]:
            self.assertIsInstance(sample(), Mapping)
            self.assertIsSubclass(sample, Mapping)
        self.validate_abstract_methods(Mapping, '__iter__', '__len__', '__getitem__')
        class MyMapping(Mapping):
            def __len__(self):
                return 0
            def __getitem__(self, i):
                raise IndexError
            def __iter__(self):
                return iter(())
        self.validate_comparison(MyMapping())
        self.assertRaises(TypeError, reversed, MyMapping())

    def test_MutableMapping(self):
        for sample in [dict]:
            self.assertIsInstance(sample(), MutableMapping)
            self.assertIsSubclass(sample, MutableMapping)
        self.validate_abstract_methods(MutableMapping, '__iter__', '__len__',
            '__getitem__', '__setitem__', '__delitem__')

    def test_MutableMapping_subclass(self):
        # Test issue 9214
        mymap = UserDict()
        mymap['red'] = 5
        self.assertIsInstance(mymap.keys(), Set)
        self.assertIsInstance(mymap.keys(), KeysView)
        self.assertIsInstance(mymap.values(), Collection)
        self.assertIsInstance(mymap.values(), ValuesView)
        self.assertIsInstance(mymap.items(), Set)
        self.assertIsInstance(mymap.items(), ItemsView)

        mymap = UserDict()
        mymap['red'] = 5
        z = mymap.keys() | {'orange'}
        self.assertIsInstance(z, set)
        list(z)
        mymap['blue'] = 7               # Shouldn't affect 'z'
        self.assertEqual(sorted(z), ['orange', 'red'])

        mymap = UserDict()
        mymap['red'] = 5
        z = mymap.items() | {('orange', 3)}
        self.assertIsInstance(z, set)
        list(z)
        mymap['blue'] = 7               # Shouldn't affect 'z'
        self.assertEqual(z, {('orange', 3), ('red', 5)})

    def test_Sequence(self):
        for sample in [tuple, list, bytes, str]:
            self.assertIsInstance(sample(), Sequence)
            self.assertIsSubclass(sample, Sequence)
        self.assertIsInstance(range(10), Sequence)
        self.assertIsSubclass(range, Sequence)
        self.assertIsInstance(memoryview(b""), Sequence)
        self.assertIsSubclass(memoryview, Sequence)
        self.assertIsSubclass(str, Sequence)
        self.validate_abstract_methods(Sequence, '__len__', '__getitem__')

    def test_Sequence_mixins(self):
        class SequenceSubclass(Sequence):
            def __init__(self, seq=()):
                self.seq = seq

            def __getitem__(self, index):
                return self.seq[index]

            def __len__(self):
                return len(self.seq)

        # Compare Sequence.index() behavior to (list|str).index() behavior
        def assert_index_same(seq1, seq2, index_args):
            try:
                expected = seq1.index(*index_args)
            except ValueError:
                with self.assertRaises(ValueError):
                    seq2.index(*index_args)
            else:
                actual = seq2.index(*index_args)
                self.assertEqual(
                    actual, expected, '%r.index%s' % (seq1, index_args))

        for ty in list, str:
            nativeseq = ty('abracadabra')
            indexes = [-10000, -9999] + list(range(-3, len(nativeseq) + 3))
            seqseq = SequenceSubclass(nativeseq)
            for letter in set(nativeseq) | {'z'}:
                assert_index_same(nativeseq, seqseq, (letter,))
                for start in range(-3, len(nativeseq) + 3):
                    assert_index_same(nativeseq, seqseq, (letter, start))
                    for stop in range(-3, len(nativeseq) + 3):
                        assert_index_same(
                            nativeseq, seqseq, (letter, start, stop))

    def test_ByteString(self):
        previous_sys_modules = sys.modules.copy()
        self.addCleanup(sys.modules.update, previous_sys_modules)

        for module in "collections", "_collections_abc", "collections.abc":
            sys.modules.pop(module, None)

        with self.assertWarns(DeprecationWarning):
            from collections.abc import ByteString
        for sample in [bytes, bytearray]:
            with self.assertWarns(DeprecationWarning):
                self.assertIsInstance(sample(), ByteString)
            self.assertTrue(issubclass(sample, ByteString))
        for sample in [str, list, tuple]:
            with self.assertWarns(DeprecationWarning):
                self.assertNotIsInstance(sample(), ByteString)
            self.assertFalse(issubclass(sample, ByteString))
        with self.assertWarns(DeprecationWarning):
            self.assertNotIsInstance(memoryview(b""), ByteString)
        self.assertFalse(issubclass(memoryview, ByteString))
        with self.assertWarns(DeprecationWarning):
            self.validate_abstract_methods(ByteString, '__getitem__', '__len__')

        with self.assertWarns(DeprecationWarning):
            class X(ByteString): pass

        with self.assertWarns(DeprecationWarning):
            # No metaclass conflict
            class Z(ByteString, Awaitable): pass

    def test_ByteString_attribute_access(self):
        collections_abc = import_fresh_module(
            "collections.abc",
            fresh=("collections", "_collections_abc")
        )
        with self.assertWarns(DeprecationWarning):
            collections_abc.ByteString

    def test_Buffer(self):
        for sample in [bytes, bytearray, memoryview]:
            self.assertIsInstance(sample(b"x"), Buffer)
            self.assertIsSubclass(sample, Buffer)
        for sample in [str, list, tuple]:
            self.assertNotIsInstance(sample(), Buffer)
            self.assertNotIsSubclass(sample, Buffer)
        self.validate_abstract_methods(Buffer, '__buffer__')

    def test_MutableSequence(self):
        for sample in [tuple, str, bytes]:
            self.assertNotIsInstance(sample(), MutableSequence)
            self.assertNotIsSubclass(sample, MutableSequence)
        for sample in [list, bytearray, deque]:
            self.assertIsInstance(sample(), MutableSequence)
            self.assertIsSubclass(sample, MutableSequence)
        self.assertIsSubclass(array.array, MutableSequence)
        self.assertNotIsSubclass(str, MutableSequence)
        self.validate_abstract_methods(MutableSequence, '__len__', '__getitem__',
                                       '__setitem__', '__delitem__', 'insert')

    def test_MutableSequence_mixins(self):
        # Test the mixins of MutableSequence by creating a minimal concrete
        # class inherited from it.
        class MutableSequenceSubclass(MutableSequence):
            def __init__(self):
                self.lst = []

            def __setitem__(self, index, value):
                self.lst[index] = value

            def __getitem__(self, index):
                return self.lst[index]

            def __len__(self):
                return len(self.lst)

            def __delitem__(self, index):
                del self.lst[index]

            def insert(self, index, value):
                self.lst.insert(index, value)

        mss = MutableSequenceSubclass()
        mss.append(0)
        mss.extend((1, 2, 3, 4))
        self.assertEqual(len(mss), 5)
        self.assertEqual(mss[3], 3)
        mss.reverse()
        self.assertEqual(mss[3], 1)
        mss.pop()
        self.assertEqual(len(mss), 4)
        mss.remove(3)
        self.assertEqual(len(mss), 3)
        mss += (10, 20, 30)
        self.assertEqual(len(mss), 6)
        self.assertEqual(mss[-1], 30)
        mss.clear()
        self.assertEqual(len(mss), 0)

        # issue 34427
        # extending self should not cause infinite loop
        items = 'ABCD'
        mss2 = MutableSequenceSubclass()
        mss2.extend(items + items)
        mss.clear()
        mss.extend(items)
        mss.extend(mss)
        self.assertEqual(len(mss), len(mss2))
        self.assertEqual(list(mss), list(mss2))

    def test_illegal_patma_flags(self):
        with self.assertRaises(TypeError):
            class Both(Collection):
                __abc_tpflags__ = (Sequence.__flags__ | Mapping.__flags__)


################################################################################
### Counter
################################################################################

class CounterSubclassWithSetItem(Counter):
    # Test a counter subclass that overrides __setitem__
    def __init__(self, *args, **kwds):
        self.called = False
        Counter.__init__(self, *args, **kwds)
    def __setitem__(self, key, value):
        self.called = True
        Counter.__setitem__(self, key, value)

class CounterSubclassWithGet(Counter):
    # Test a counter subclass that overrides get()
    def __init__(self, *args, **kwds):
        self.called = False
        Counter.__init__(self, *args, **kwds)
    def get(self, key, default):
        self.called = True
        return Counter.get(self, key, default)

class TestCounter(unittest.TestCase):

    def test_basics(self):
        c = Counter('abcaba')
        self.assertEqual(c, Counter({'a':3 , 'b': 2, 'c': 1}))
        self.assertEqual(c, Counter(a=3, b=2, c=1))
        self.assertIsInstance(c, dict)
        self.assertIsInstance(c, Mapping)
        self.assertIsSubclass(Counter, dict)
        self.assertIsSubclass(Counter, Mapping)
        self.assertEqual(len(c), 3)
        self.assertEqual(sum(c.values()), 6)
        self.assertEqual(list(c.values()), [3, 2, 1])
        self.assertEqual(list(c.keys()), ['a', 'b', 'c'])
        self.assertEqual(list(c), ['a', 'b', 'c'])
        self.assertEqual(list(c.items()),
                         [('a', 3), ('b', 2), ('c', 1)])
        self.assertEqual(c['b'], 2)
        self.assertEqual(c['z'], 0)
        self.assertEqual(c.__contains__('c'), True)
        self.assertEqual(c.__contains__('z'), False)
        self.assertEqual(c.get('b', 10), 2)
        self.assertEqual(c.get('z', 10), 10)
        self.assertEqual(c, dict(a=3, b=2, c=1))
        self.assertEqual(repr(c), "Counter({'a': 3, 'b': 2, 'c': 1})")
        self.assertEqual(c.most_common(), [('a', 3), ('b', 2), ('c', 1)])
        for i in range(5):
            self.assertEqual(c.most_common(i),
                             [('a', 3), ('b', 2), ('c', 1)][:i])
        self.assertEqual(''.join(c.elements()), 'aaabbc')
        c['a'] += 1         # increment an existing value
        c['b'] -= 2         # sub existing value to zero
        del c['c']          # remove an entry
        del c['c']          # make sure that del doesn't raise KeyError
        c['d'] -= 2         # sub from a missing value
        c['e'] = -5         # directly assign a missing value
        c['f'] += 4         # add to a missing value
        self.assertEqual(c, dict(a=4, b=0, d=-2, e=-5, f=4))
        self.assertEqual(''.join(c.elements()), 'aaaaffff')
        self.assertEqual(c.pop('f'), 4)
        self.assertNotIn('f', c)
        for i in range(3):
            elem, cnt = c.popitem()
            self.assertNotIn(elem, c)
        c.clear()
        self.assertEqual(c, {})
        self.assertEqual(repr(c), 'Counter()')
        self.assertRaises(NotImplementedError, Counter.fromkeys, 'abc')
        self.assertRaises(TypeError, hash, c)
        c.update(dict(a=5, b=3))
        c.update(c=1)
        c.update(Counter('a' * 50 + 'b' * 30))
        c.update()          # test case with no args
        c.__init__('a' * 500 + 'b' * 300)
        c.__init__('cdc')
        c.__init__()
        self.assertEqual(c, dict(a=555, b=333, c=3, d=1))
        self.assertEqual(c.setdefault('d', 5), 1)
        self.assertEqual(c['d'], 1)
        self.assertEqual(c.setdefault('e', 5), 5)
        self.assertEqual(c['e'], 5)

    def test_update_reentrant_add_clears_counter(self):
        c = Counter()
        key = object()

        class Evil(int):
            def __add__(self, other):
                c.clear()
                return NotImplemented

        c[key] = Evil()
        c.update([key])
        self.assertEqual(c[key], 1)

    def test_init(self):
        self.assertEqual(list(Counter(self=42).items()), [('self', 42)])
        self.assertEqual(list(Counter(iterable=42).items()), [('iterable', 42)])
        self.assertEqual(list(Counter(iterable=None).items()), [('iterable', None)])
        self.assertRaises(TypeError, Counter, 42)
        self.assertRaises(TypeError, Counter, (), ())
        self.assertRaises(TypeError, Counter.__init__)

    def test_total(self):
        c = Counter(a=10, b=5, c=0)
        self.assertEqual(c.total(), 15)

    def test_order_preservation(self):
        # Input order dictates items() order
        self.assertEqual(list(Counter('abracadabra').items()),
               [('a', 5), ('b', 2), ('r', 2), ('c', 1), ('d', 1)])
        # letters with same count:   ^----------^         ^---------^

        # Verify retention of order even when all counts are equal
        self.assertEqual(list(Counter('xyzpdqqdpzyx').items()),
               [('x', 2), ('y', 2), ('z', 2), ('p', 2), ('d', 2), ('q', 2)])

        # Input order dictates elements() order
        self.assertEqual(list(Counter('abracadabra simsalabim').elements()),
                ['a', 'a', 'a', 'a', 'a', 'a', 'a', 'b', 'b', 'b','r',
                 'r', 'c', 'd', ' ', 's', 's', 'i', 'i', 'm', 'm', 'l'])

        # Math operations order first by the order encountered in the left
        # operand and then by the order encountered in the right operand.
        ps = 'aaabbcdddeefggghhijjjkkl'
        qs = 'abbcccdeefffhkkllllmmnno'
        order = {letter: i for i, letter in enumerate(dict.fromkeys(ps + qs))}
        def correctly_ordered(seq):
            'Return true if the letters occur in the expected order'
            positions = [order[letter] for letter in seq]
            return positions == sorted(positions)

        p, q = Counter(ps), Counter(qs)
        self.assertTrue(correctly_ordered(+p))
        self.assertTrue(correctly_ordered(-p))
        self.assertTrue(correctly_ordered(p + q))
        self.assertTrue(correctly_ordered(p - q))
        self.assertTrue(correctly_ordered(p | q))
        self.assertTrue(correctly_ordered(p & q))
        self.assertTrue(correctly_ordered(p ^ q))

        p, q = Counter(ps), Counter(qs)
        p += q
        self.assertTrue(correctly_ordered(p))

        p, q = Counter(ps), Counter(qs)
        p -= q
        self.assertTrue(correctly_ordered(p))

        p, q = Counter(ps), Counter(qs)
        p |= q
        self.assertTrue(correctly_ordered(p))

        p, q = Counter(ps), Counter(qs)
        p &= q
        self.assertTrue(correctly_ordered(p))

        p, q = Counter(ps), Counter(qs)
        p ^= q
        self.assertTrue(correctly_ordered(p))

        p, q = Counter(ps), Counter(qs)
        p.update(q)
        self.assertTrue(correctly_ordered(p))

        p, q = Counter(ps), Counter(qs)
        p.subtract(q)
        self.assertTrue(correctly_ordered(p))

    def test_update(self):
        c = Counter()
        c.update(self=42)
        self.assertEqual(list(c.items()), [('self', 42)])
        c = Counter()
        c.update(iterable=42)
        self.assertEqual(list(c.items()), [('iterable', 42)])
        c = Counter()
        c.update(iterable=None)
        self.assertEqual(list(c.items()), [('iterable', None)])
        self.assertRaises(TypeError, Counter().update, 42)
        self.assertRaises(TypeError, Counter().update, {}, {})
        self.assertRaises(TypeError, Counter.update)

    def test_copying(self):
        # Check that counters are copyable, deepcopyable, picklable, and
        #have a repr/eval round-trip
        words = Counter('which witch had which witches wrist watch'.split())
        def check(dup):
            msg = "\ncopy: %s\nwords: %s" % (dup, words)
            self.assertIsNot(dup, words, msg)
            self.assertEqual(dup, words)
        check(words.copy())
        check(copy.copy(words))
        check(copy.deepcopy(words))
        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
            with self.subTest(proto=proto):
                check(pickle.loads(pickle.dumps(words, proto)))
        check(eval(repr(words)))
        update_test = Counter()
        update_test.update(words)
        check(update_test)
        check(Counter(words))

    def test_copy_subclass(self):
        class MyCounter(Counter):
            pass
        c = MyCounter('slartibartfast')
        d = c.copy()
        self.assertEqual(d, c)
        self.assertEqual(len(d), len(c))
        self.assertEqual(type(d), type(c))

    def test_conversions(self):
        # Convert to: set, list, dict
        s = 'she sells sea shells by the sea shore'
        self.assertEqual(sorted(Counter(s).elements()), sorted(s))
        self.assertEqual(sorted(Counter(s)), sorted(set(s)))
        self.assertEqual(dict(Counter(s)), dict(Counter(s).items()))
        self.assertEqual(set(Counter(s)), set(s))

    def test_invariant_for_the_in_operator(self):
        c = Counter(a=10, b=-2, c=0)
        for elem in c:
            self.assertTrue(elem in c)
            self.assertIn(elem, c)

    def test_multiset_operations(self):
        # Verify that adding a zero counter will strip zeros and negatives
        c = Counter(a=10, b=-2, c=0) + Counter()
        self.assertEqual(dict(c), dict(a=10))

        elements = 'abcd'
        for i in range(1000):
            # test random pairs of multisets
            p = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            p.update(e=1, f=-1, g=0)
            q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            q.update(h=1, i=-1, j=0)
            for counterop, numberop in [
                (Counter.__add__, lambda x, y: max(0, x+y)),
                (Counter.__sub__, lambda x, y: max(0, x-y)),
                (Counter.__or__, lambda x, y: max(0,x,y)),
                (Counter.__and__, lambda x, y: max(0, min(x,y))),
                (Counter.__xor__, lambda x, y: max(0, max(x,y) - min(x,y))),
            ]:
                result = counterop(p, q)
                for x in elements:
                    self.assertEqual(numberop(p[x], q[x]), result[x],
                                     (counterop, x, p, q))
                # verify that results exclude non-positive counts
                self.assertTrue(x>0 for x in result.values())

        elements = 'abcdef'
        for i in range(100):
            # verify that random multisets with no repeats are exactly like sets
            p = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            q = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            for counterop, setop in [
                (Counter.__sub__, set.__sub__),
                (Counter.__or__, set.__or__),
                (Counter.__and__, set.__and__),
                (Counter.__xor__, set.__xor__),
            ]:
                counter_result = counterop(p, q)
                set_result = setop(set(p.elements()), set(q.elements()))
                self.assertEqual(counter_result, dict.fromkeys(set_result, 1))

    def test_inplace_operations(self):
        elements = 'abcd'
        for i in range(1000):
            # test random pairs of multisets
            p = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            p.update(e=1, f=-1, g=0)
            q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            q.update(h=1, i=-1, j=0)
            for inplace_op, regular_op in [
                (Counter.__iadd__, Counter.__add__),
                (Counter.__isub__, Counter.__sub__),
                (Counter.__ior__, Counter.__or__),
                (Counter.__iand__, Counter.__and__),
                (Counter.__ixor__, Counter.__xor__),
            ]:
                c = p.copy()
                c_id = id(c)
                regular_result = regular_op(c, q)
                inplace_result = inplace_op(c, q)
                self.assertEqual(inplace_result, regular_result)
                self.assertEqual(id(inplace_result), c_id)

    def test_subtract(self):
        c = Counter(a=-5, b=0, c=5, d=10, e=15,g=40)
        c.subtract(a=1, b=2, c=-3, d=10, e=20, f=30, h=-50)
        self.assertEqual(c, Counter(a=-6, b=-2, c=8, d=0, e=-5, f=-30, g=40, h=50))
        c = Counter(a=-5, b=0, c=5, d=10, e=15,g=40)
        c.subtract(Counter(a=1, b=2, c=-3, d=10, e=20, f=30, h=-50))
        self.assertEqual(c, Counter(a=-6, b=-2, c=8, d=0, e=-5, f=-30, g=40, h=50))
        c = Counter('aaabbcd')
        c.subtract('aaaabbcce')
        self.assertEqual(c, Counter(a=-1, b=0, c=-1, d=1, e=-1))

        c = Counter()
        c.subtract(self=42)
        self.assertEqual(list(c.items()), [('self', -42)])
        c = Counter()
        c.subtract(iterable=42)
        self.assertEqual(list(c.items()), [('iterable', -42)])
        self.assertRaises(TypeError, Counter().subtract, 42)
        self.assertRaises(TypeError, Counter().subtract, {}, {})
        self.assertRaises(TypeError, Counter.subtract)

    def test_unary(self):
        c = Counter(a=-5, b=0, c=5, d=10, e=15,g=40)
        self.assertEqual(dict(+c), dict(c=5, d=10, e=15, g=40))
        self.assertEqual(dict(-c), dict(a=5))

    def test_repr_nonsortable(self):
        c = Counter(a=2, b=None)
        r = repr(c)
        self.assertIn("'a': 2", r)
        self.assertIn("'b': None", r)

    def test_helper_function(self):
        # two paths, one for real dicts and one for other mappings
        elems = list('abracadabra')

        d = dict()
        _count_elements(d, elems)
        self.assertEqual(d, {'a': 5, 'r': 2, 'b': 2, 'c': 1, 'd': 1})

        m = OrderedDict()
        _count_elements(m, elems)
        self.assertEqual(m,
             OrderedDict([('a', 5), ('b', 2), ('r', 2), ('c', 1), ('d', 1)]))

        # test fidelity to the pure python version
        c = CounterSubclassWithSetItem('abracadabra')
        self.assertTrue(c.called)
        self.assertEqual(dict(c), {'a': 5, 'b': 2, 'c': 1, 'd': 1, 'r':2 })
        c = CounterSubclassWithGet('abracadabra')
        self.assertTrue(c.called)
        self.assertEqual(dict(c), {'a': 5, 'b': 2, 'c': 1, 'd': 1, 'r':2 })

    def test_multiset_operations_equivalent_to_set_operations(self):
        # When the multiplicities are all zero or one, multiset operations
        # are guaranteed to be equivalent to the corresponding operations
        # for regular sets.
        s = list(product(('a', 'b', 'c'), range(2)))
        powerset = chain.from_iterable(combinations(s, r) for r in range(len(s)+1))
        counters = [Counter(dict(groups)) for groups in powerset]
        for cp, cq in product(counters, repeat=2):
            sp = set(cp.elements())
            sq = set(cq.elements())
            self.assertEqual(set(cp + cq), sp | sq)
            self.assertEqual(set(cp - cq), sp - sq)
            self.assertEqual(set(cp | cq), sp | sq)
            self.assertEqual(set(cp & cq), sp & sq)
            self.assertEqual(set(cp ^ cq), sp ^ sq)
            self.assertEqual(cp == cq, sp == sq)
            self.assertEqual(cp != cq, sp != sq)
            self.assertEqual(cp <= cq, sp <= sq)
            self.assertEqual(cp >= cq, sp >= sq)
            self.assertEqual(cp < cq, sp < sq)
            self.assertEqual(cp > cq, sp > sq)

    def test_eq(self):
        self.assertEqual(Counter(a=3, b=2, c=0), Counter('ababa'))
        self.assertNotEqual(Counter(a=3, b=2), Counter('babab'))

    def test_le(self):
        self.assertTrue(Counter(a=3, b=2, c=0) <= Counter('ababa'))
        self.assertTrue(Counter() <= Counter(c=1))
        self.assertFalse(Counter() <= Counter(c=-1))
        self.assertFalse(Counter(a=3, b=2) <= Counter('babab'))

    def test_lt(self):
        self.assertTrue(Counter(a=3, b=1, c=0) < Counter('ababa'))
        self.assertFalse(Counter(a=3, b=2, c=0) < Counter('ababa'))

    def test_ge(self):
        self.assertTrue(Counter(a=2, b=1, c=0) >= Counter('aab'))
        self.assertTrue(Counter() >= Counter(c=-1))
        self.assertFalse(Counter() >= Counter(c=1))
        self.assertFalse(Counter(a=3, b=2, c=0) >= Counter('aabd'))

    def test_gt(self):
        self.assertTrue(Counter(a=3, b=2, c=0) > Counter('aab'))
        self.assertFalse(Counter(a=2, b=1, c=0) > Counter('aab'))

    def test_symmetric_difference(self):
        population = (-4, -3, -2, -1, 0, 1, 2, 3, 4)

        for a, b1, b2, c in product(population, repeat=4):
            p = Counter(a=a, b=b1)
            q = Counter(b=b2, c=c)
            r = p ^ q

            # Elementwise invariants
            for k in ('a', 'b', 'c'):
                self.assertEqual(r[k], max(p[k], q[k]) - min(p[k], q[k]))
                self.assertEqual(r[k], abs(p[k] - q[k]))

            # Invariant for all positive, negative, and zero counts
            self.assertEqual(r, (p - q) | (q - p))

            # Invariant for non-negative counts
            if a >= 0 and b1 >= 0 and b2 >= 0 and c >= 0:
                self.assertEqual(r, (p | q) - (p & q))

            # Zeros and negatives eliminated
            self.assertTrue(all(value > 0 for value in r.values()))

            # Output preserves input order:  p first and then q
            keys = list(p) + list(q)
            indices = [keys.index(k) for k in r]
            self.assertEqual(indices, sorted(indices))

            # Inplace operation matches binary operation
            pp = Counter(p)
            qq = Counter(q)
            pp ^= qq
            self.assertEqual(pp, r)


def load_tests(loader, tests, pattern):
    tests.addTest(doctest.DocTestSuite(collections))
    return tests


if __name__ == "__main__":
    unittest.main()