Doc/library/binascii.rst

:mod:`!binascii` --- Convert between binary and ASCII
=====================================================

.. module:: binascii
   :synopsis: Tools for converting between binary and various ASCII-encoded binary
              representations.

.. index::
   pair: module; base64

--------------

The :mod:`!binascii` module contains a number of methods to convert between
binary and various ASCII-encoded binary representations. Normally, you will not
use these functions directly but use wrapper modules like
:mod:`base64` instead. The :mod:`!binascii` module contains
low-level functions written in C for greater speed that are used by the
higher-level modules.

.. note::

   ``a2b_*`` functions accept Unicode strings containing only ASCII characters.
   Other functions only accept :term:`bytes-like objects <bytes-like object>` (such as
   :class:`bytes`, :class:`bytearray` and other objects that support the buffer
   protocol).

   .. versionchanged:: 3.3
      ASCII-only unicode strings are now accepted by the ``a2b_*`` functions.


The :mod:`!binascii` module defines the following functions:


.. function:: a2b_uu(string)

   Convert a single line of uuencoded data back to binary and return the binary
   data. Lines normally contain 45 (binary) bytes, except for the last line. Line
   data may be followed by whitespace.


.. function:: b2a_uu(data, *, backtick=False)

   Convert binary data to a line of ASCII characters, the return value is the
   converted line, including a newline char. The length of *data* should be at most
   45. If *backtick* is true, zeros are represented by ``'`'`` instead of spaces.

   .. versionchanged:: 3.7
      Added the *backtick* parameter.


.. function:: a2b_base64(string, /, *, alphabet=BASE64_ALPHABET, strict_mode=False)
              a2b_base64(string, /, *, ignorechars, alphabet=BASE64_ALPHABET, strict_mode=True)

   Convert a block of base64 data back to binary and return the binary data. More
   than one line may be passed at a time.

   Optional *alphabet* must be a :class:`bytes` object of length 64 which
   specifies an alternative alphabet.

   If *ignorechars* is specified, it should be a :term:`bytes-like object`
   containing characters to ignore from the input when *strict_mode* is true.
   If *ignorechars* contains the pad character ``'='``,  the pad characters
   presented before the end of the encoded data and the excess pad characters
   will be ignored.
   The default value of *strict_mode* is ``True`` if *ignorechars* is specified,
   ``False`` otherwise.

   If *strict_mode* is true, only valid base64 data will be converted. Invalid base64
   data will raise :exc:`binascii.Error`.

   Valid base64:

   * Conforms to :rfc:`4648`.
   * Contains only characters from the base64 alphabet.
   * Contains no excess data after padding (including excess padding, newlines, etc.).
   * Does not start with a padding.

   .. versionchanged:: 3.11
      Added the *strict_mode* parameter.

   .. versionchanged:: 3.15
      Added the *alphabet* and *ignorechars* parameters.


.. function:: b2a_base64(data, *, alphabet=BASE64_ALPHABET, wrapcol=0, newline=True)

   Convert binary data to a line(s) of ASCII characters in base64 coding,
   as specified in :rfc:`4648`.

   If *wrapcol* is non-zero, insert a newline (``b'\n'``) character
   after at most every *wrapcol* characters.
   If *wrapcol* is zero (default), do not insert any newlines.

   If *newline* is true (default), a newline character will be added
   at the end of the output.

   .. versionchanged:: 3.6
      Added the *newline* parameter.

   .. versionchanged:: 3.15
      Added the *alphabet* and *wrapcol* parameters.


.. function:: a2b_ascii85(string, /, *, foldspaces=False, adobe=False, ignorechars=b"")

   Convert Ascii85 data back to binary and return the binary data.

   Valid Ascii85 data contains characters from the Ascii85 alphabet in groups
   of five (except for the final group, which may have from two to five
   characters). Each group encodes 32 bits of binary data in the range from
   ``0`` to ``2 ** 32 - 1``, inclusive. The special character ``z`` is
   accepted as a short form of the group ``!!!!!``, which encodes four
   consecutive null bytes.

   *foldspaces* is a flag that specifies whether the 'y' short sequence
   should be accepted as shorthand for 4 consecutive spaces (ASCII 0x20).
   This feature is not supported by the "standard" Ascii85 encoding.

   *adobe* controls whether the input sequence is in Adobe Ascii85 format
   (i.e. is framed with <~ and ~>).

   *ignorechars* should be a :term:`bytes-like object` containing characters
   to ignore from the input.
   This should only contain whitespace characters.

   Invalid Ascii85 data will raise :exc:`binascii.Error`.

   .. versionadded:: 3.15


.. function:: b2a_ascii85(data, /, *, foldspaces=False, wrapcol=0, pad=False, adobe=False)

   Convert binary data to a formatted sequence of ASCII characters in Ascii85
   coding. The return value is the converted data.

   *foldspaces* is an optional flag that uses the special short sequence 'y'
   instead of 4 consecutive spaces (ASCII 0x20) as supported by 'btoa'. This
   feature is not supported by the "standard" Ascii85 encoding.

   If *wrapcol* is non-zero, insert a newline (``b'\n'``) character
   after at most every *wrapcol* characters.
   If *wrapcol* is zero (default), do not insert any newlines.

   If *pad* is true, the input is padded with ``b'\0'`` so its length is a
   multiple of 4 bytes before encoding.
   Note that the ``btoa`` implementation always pads.

   *adobe* controls whether the encoded byte sequence is framed with ``<~``
   and ``~>``, which is used by the Adobe implementation.

   .. versionadded:: 3.15


.. function:: a2b_base85(string, /, *, alphabet=BASE85_ALPHABET)

   Convert Base85 data back to binary and return the binary data.
   More than one line may be passed at a time.

   Valid Base85 data contains characters from the Base85 alphabet in groups
   of five (except for the final group, which may have from two to five
   characters). Each group encodes 32 bits of binary data in the range from
   ``0`` to ``2 ** 32 - 1``, inclusive.

   Optional *alphabet* must be a :class:`bytes` object of length 85 which
   specifies an alternative alphabet.

   Invalid Base85 data will raise :exc:`binascii.Error`.

   .. versionadded:: 3.15


.. function:: b2a_base85(data, /, *, alphabet=BASE85_ALPHABET, pad=False)

   Convert binary data to a line of ASCII characters in Base85 coding.
   The return value is the converted line.

   Optional *alphabet* must be a :term:`bytes-like object` of length 85 which
   specifies an alternative alphabet.

   If *pad* is true, the input is padded with ``b'\0'`` so its length is a
   multiple of 4 bytes before encoding.

   .. versionadded:: 3.15


.. function:: a2b_base32(string, /, *, alphabet=BASE32_ALPHABET)

   Convert base32 data back to binary and return the binary data.

   Valid base32 data contains characters from the base32 alphabet specified
   in :rfc:`4648` in groups of eight (if necessary, the final group is padded
   to eight characters with ``=``). Each group encodes 40 bits of binary data
   in the range from ``0`` to ``2 ** 40 - 1``, inclusive.

   .. note::
      This function does not map lowercase characters (which are invalid in
      standard base32) to their uppercase counterparts, nor does it
      contextually map ``0`` to ``O`` and ``1`` to ``I``/``L`` as :rfc:`4648`
      allows.

   Optional *alphabet* must be a :class:`bytes` object of length 32 which
   specifies an alternative alphabet.

   Invalid base32 data will raise :exc:`binascii.Error`.

   .. versionadded:: next

.. function:: b2a_base32(data, /, *, alphabet=BASE32_ALPHABET)

   Convert binary data to a line of ASCII characters in base32 coding,
   as specified in :rfc:`4648`. The return value is the converted line.

   Optional *alphabet* must be a :term:`bytes-like object` of length 32 which
   specifies an alternative alphabet.

   .. versionadded:: next

.. function:: a2b_qp(data, header=False)

   Convert a block of quoted-printable data back to binary and return the binary
   data. More than one line may be passed at a time. If the optional argument
   *header* is present and true, underscores will be decoded as spaces.


.. function:: b2a_qp(data, quotetabs=False, istext=True, header=False)

   Convert binary data to a line(s) of ASCII characters in quoted-printable
   encoding.  The return value is the converted line(s). If the optional argument
   *quotetabs* is present and true, all tabs and spaces will be encoded.   If the
   optional argument *istext* is present and true, newlines are not encoded but
   trailing whitespace will be encoded. If the optional argument *header* is
   present and true, spaces will be encoded as underscores per :rfc:`1522`. If the
   optional argument *header* is present and false, newline characters will be
   encoded as well; otherwise linefeed conversion might corrupt the binary data
   stream.


.. function:: crc_hqx(data, value)

   Compute a 16-bit CRC value of *data*, starting with *value* as the
   initial CRC, and return the result.  This uses the CRC-CCITT polynomial
   *x*:sup:`16` + *x*:sup:`12` + *x*:sup:`5` + 1, often represented as
   0x1021.  This CRC is used in the binhex4 format.


.. function:: crc32(data[, value])

   Compute CRC-32, the unsigned 32-bit checksum of *data*, starting with an
   initial CRC of *value*.  The default initial CRC is zero.  The algorithm
   is consistent with the ZIP file checksum.  Since the algorithm is designed for
   use as a checksum algorithm, it is not suitable for use as a general hash
   algorithm.  Use as follows::

      print(binascii.crc32(b"hello world"))
      # Or, in two pieces:
      crc = binascii.crc32(b"hello")
      crc = binascii.crc32(b" world", crc)
      print('crc32 = {:#010x}'.format(crc))

   .. versionchanged:: 3.0
      The result is always unsigned.

.. function:: b2a_hex(data[, sep[, bytes_per_sep=1]])
              hexlify(data[, sep[, bytes_per_sep=1]])

   Return the hexadecimal representation of the binary *data*.  Every byte of
   *data* is converted into the corresponding 2-digit hex representation.  The
   returned bytes object is therefore twice as long as the length of *data*.

   Similar functionality (but returning a text string) is also conveniently
   accessible using the :meth:`bytes.hex` method.

   If *sep* is specified, it must be a single character str or bytes object.
   It will be inserted in the output after every *bytes_per_sep* input bytes.
   Separator placement is counted from the right end of the output by default,
   if you wish to count from the left, supply a negative *bytes_per_sep* value.

      >>> import binascii
      >>> binascii.b2a_hex(b'\xb9\x01\xef')
      b'b901ef'
      >>> binascii.hexlify(b'\xb9\x01\xef', '-')
      b'b9-01-ef'
      >>> binascii.b2a_hex(b'\xb9\x01\xef', b'_', 2)
      b'b9_01ef'
      >>> binascii.b2a_hex(b'\xb9\x01\xef', b' ', -2)
      b'b901 ef'

   .. versionchanged:: 3.8
      The *sep* and *bytes_per_sep* parameters were added.

.. function:: a2b_hex(hexstr)
              unhexlify(hexstr)

   Return the binary data represented by the hexadecimal string *hexstr*.  This
   function is the inverse of :func:`b2a_hex`. *hexstr* must contain an even number
   of hexadecimal digits (which can be upper or lower case), otherwise an
   :exc:`Error` exception is raised.

   Similar functionality (accepting only text string arguments, but more
   liberal towards whitespace) is also accessible using the
   :meth:`bytes.fromhex` class method.

.. exception:: Error

   Exception raised on errors. These are usually programming errors.


.. exception:: Incomplete

   Exception raised on incomplete data. These are usually not programming errors,
   but may be handled by reading a little more data and trying again.


.. data:: BASE64_ALPHABET

   The Base 64 alphabet according to :rfc:`4648`.

   .. versionadded:: next

.. data:: URLSAFE_BASE64_ALPHABET

   The "URL and filename safe" Base 64 alphabet according to :rfc:`4648`.

   .. versionadded:: next

.. data:: UU_ALPHABET

   The uuencoding alphabet.

   .. versionadded:: next

.. data:: CRYPT_ALPHABET

   The Base 64 alphabet used in the :manpage:`crypt(3)` routine and in the GEDCOM format.

   .. versionadded:: next

.. data:: BINHEX_ALPHABET

   The Base 64 alphabet used in BinHex 4 (HQX) within the classic Mac OS.

   .. versionadded:: next

.. data:: BASE85_ALPHABET

   The Base85 alphabet.

   .. versionadded:: next

.. data:: ASCII85_ALPHABET

   The Ascii85 alphabet.

   .. versionadded:: next

.. data:: Z85_ALPHABET

   The `Z85 <https://rfc.zeromq.org/spec/32/>`_ alphabet.

   .. versionadded:: next

.. data:: BASE32_ALPHABET

   The Base 32 alphabet according to :rfc:`4648`.

   .. versionadded:: next

.. data:: BASE32HEX_ALPHABET

   The "Extended Hex" Base 32 alphabet according to :rfc:`4648`.
   Data encoded with this alphabet maintains its sort order during bitwise
   comparisons.

   .. versionadded:: next


.. seealso::

   Module :mod:`base64`
      Support for RFC compliant base64-style encoding in base 16, 32, 64,
      and 85.

   Module :mod:`quopri`
      Support for quoted-printable encoding used in MIME email messages.