google/appengine/tools/devappserver2/python/pdb_sandbox.py

#!/usr/bin/env python
#
# Copyright 2007 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
"""Modify pdb to work with the devappserver2 sandbox."""

import sys

def install():
  """Install the necessary changes to pdb.

  Monkeypatch pdb so that it can be used in the devappserver sandbox. Must
  be called after the sandbox has been installed but before stdin/stdout
  objects have been reassigned.
  """
  # Import here (i.e. after sandbox installed) to get the post sandbox pdb.
  # Extremely important so that we monkeypatch the same pdb the apps can
  # import.
  import pdb as pdb_postsandbox

  # Save stdin/stdout as the references will not be available when user
  # code runs.
  real_stdin = sys.stdin
  real_stdout = sys.stdout

  # Capture the original Pdb so we can forward the __init__ call after
  # monkeypatching (if not captured, forwarding the call results in infinite
  # recursion).
  pdb_premonkeypatch = pdb_postsandbox.Pdb

  class _Pdb(pdb_postsandbox.Pdb):
    # TODO: improve argument handling so if new arguments are added
    # in the future or the defaults change, this does not need to be updated.
    def __init__(self, completekey='tab', stdin=None, stdout=None, skip=None):
      if stdin is None:
        stdin = real_stdin
      if stdout is None:
        stdout = real_stdout
      # Pdb is old style class so no super().
      pdb_premonkeypatch.__init__(self, completekey, stdin, stdout, skip)

  pdb_postsandbox.Pdb = _Pdb