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

====================================================

.. module:: binascii

   :synopsis: Tools for converting between binary and various ASCII-encoded binary

              representations.

.. index::

   module: uu

   module: base64

   module: binhex

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:`uu`,

:mod:`base64`, or :mod:`binhex` instead. The :mod:`binascii` module contains

low-level functions written in C for greater speed that are used by the

higher-level modules.

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)

   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.

.. function:: a2b_base64(string)

   Convert a block of base64 data back to binary and return the binary data. More

   than one line may be passed at a time.

.. function:: b2a_base64(data)

   Convert binary data to a line of ASCII characters in base64 coding. The return

   value is the converted line, including a newline char. The length of *data*

   should be at most 57 to adhere to the base64 standard.

.. function:: a2b_qp(string[, header])

   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, istext, header])

   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 RFC1522. 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:: a2b_hqx(string)

   Convert binhex4 formatted ASCII data to binary, without doing RLE-decompression.

   The string should contain a complete number of binary bytes, or (in case of the

   last portion of the binhex4 data) have the remaining bits zero.

.. function:: rledecode_hqx(data)

   Perform RLE-decompression on the data, as per the binhex4 standard. The

   algorithm uses ``0x90`` after a byte as a repeat indicator, followed by a count.

   A count of ``0`` specifies a byte value of ``0x90``. The routine returns the

   decompressed data, unless data input data ends in an orphaned repeat indicator,

   in which case the :exc:`Incomplete` exception is raised.

.. function:: rlecode_hqx(data)

   Perform binhex4 style RLE-compression on *data* and return the result.

.. function:: b2a_hqx(data)

   Perform hexbin4 binary-to-ASCII translation and return the resulting string. The

   argument should already be RLE-coded, and have a length divisible by 3 (except

   possibly the last fragment).

.. function:: crc_hqx(data, crc)

   Compute the binhex4 crc value of *data*, starting with an initial *crc* and

   returning the result.

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

   Compute CRC-32, the 32-bit checksum of data, starting with an initial crc.  This

   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("hello world")

      # Or, in two pieces:

      crc = binascii.crc32("hello")

      crc = binascii.crc32(" world", crc)

      print crc

.. function:: b2a_hex(data)

              hexlify(data)

   Return the hexadecimal representation of the binary *data*.  Every byte of

   *data* is converted into the corresponding 2-digit hex representation.  The

   resulting string is therefore twice as long as the length of *data*.

.. 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 a

   :exc:`TypeError` is raised.

.. 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.

.. seealso::

   Module :mod:`base64`

      Support for base64 encoding used in MIME email messages.

   Module :mod:`binhex`

      Support for the binhex format used on the Macintosh.

   Module :mod:`uu`

      Support for UU encoding used on Unix.

   Module :mod:`quopri`

      Support for quoted-printable encoding used in MIME email messages.