cpython/Doc/library/zlib.rst

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:mod:`zlib` --- Compression compatible with :program:`gzip`
===========================================================
.. module:: zlib
:synopsis: Low-level interface to compression and decompression routines
compatible with gzip.
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For applications that require data compression, the functions in this module
allow compression and decompression, using the zlib library. The zlib library
has its own home page at http://www.zlib.net. There are known
incompatibilities between the Python module and versions of the zlib library
earlier than 1.1.3; 1.1.3 has a security vulnerability, so we recommend using
1.1.4 or later.
zlib's functions have many options and often need to be used in a particular
order. This documentation doesn't attempt to cover all of the permutations;
consult the zlib manual at http://www.zlib.net/manual.html for authoritative
information.
For reading and writing ``.gz`` files see the :mod:`gzip` module.
Merged revisions 58817-58861 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r58822 | brett.cannon | 2007-11-02 23:47:02 -0700 (Fri, 02 Nov 2007) | 2 lines Add a missing quotation mark. ........ r58840 | skip.montanaro | 2007-11-04 07:56:52 -0800 (Sun, 04 Nov 2007) | 2 lines Note change to get_dialect semantics in 2.5. Will backport to 2.5. ........ r58844 | georg.brandl | 2007-11-04 09:43:49 -0800 (Sun, 04 Nov 2007) | 2 lines Fix syntax for versionchanged markup. ........ r58850 | gregory.p.smith | 2007-11-04 18:32:26 -0800 (Sun, 04 Nov 2007) | 9 lines Fixes bug 477182 on pybsddb.sf.net. DB objects now load the flags and pay attention to them when opening an existing database. This means that d[] behaves properly even on databases previously created with DB_DUP or DB_DUPSORT flags to allow duplicate keys. http://sourceforge.net/tracker/index.php?func=detail&aid=477182&group_id=13900&atid=113900 Do not backport, this bugfix could be considered an API change. ........ r58851 | gregory.p.smith | 2007-11-04 18:56:31 -0800 (Sun, 04 Nov 2007) | 3 lines Add the bsddb.db.DBEnv.lock_id_free method. Improve test_lock's tempdir creation and cleanup. ........ r58852 | gregory.p.smith | 2007-11-05 01:06:28 -0800 (Mon, 05 Nov 2007) | 3 lines * db->get_types is only available in BerkeleyDB >= 4.2 * get compiling with older versions of python again for a stand alone release. ........ r58853 | gregory.p.smith | 2007-11-05 01:07:40 -0800 (Mon, 05 Nov 2007) | 2 lines * db->get_flags is only available in BerkeleyDB >= 4.2 ........ r58854 | mark.summerfield | 2007-11-05 01:22:48 -0800 (Mon, 05 Nov 2007) | 3 lines Added cross-references between the various archive file formats. ........ r58857 | mark.summerfield | 2007-11-05 06:38:50 -0800 (Mon, 05 Nov 2007) | 5 lines Clarified the fact that you can have comments for individual archive members even though comments to the archive itself aren't currently supported. ........
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The available exception and functions in this module are:
.. exception:: error
Exception raised on compression and decompression errors.
Merged revisions 68450,68480-68481,68493,68495,68501,68512,68514-68515,68534-68536,68552,68563,68570-68572,68575,68582,68596,68623-68624,68628 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r68450 | jeffrey.yasskin | 2009-01-09 10:47:07 -0600 (Fri, 09 Jan 2009) | 3 lines Fix issue 4884, preventing a crash in the socket code when python is compiled with llvm-gcc and run with a glibc <2.10. ........ r68480 | vinay.sajip | 2009-01-10 07:38:04 -0600 (Sat, 10 Jan 2009) | 1 line Minor documentation changes cross-referencing NullHandler to the documentation on configuring logging in a library. ........ r68481 | vinay.sajip | 2009-01-10 07:42:04 -0600 (Sat, 10 Jan 2009) | 1 line Corrected an incorrect self-reference. ........ r68493 | benjamin.peterson | 2009-01-10 11:18:55 -0600 (Sat, 10 Jan 2009) | 1 line rewrite verbose conditionals ........ r68495 | benjamin.peterson | 2009-01-10 11:36:44 -0600 (Sat, 10 Jan 2009) | 1 line tp_iter only exists with Py_TPFLAGS_HAVE_ITER #4901 ........ r68501 | vinay.sajip | 2009-01-10 13:22:57 -0600 (Sat, 10 Jan 2009) | 1 line Corrected minor typo and added .currentmodule directives to fix missing cross-references. ........ r68512 | benjamin.peterson | 2009-01-10 16:42:10 -0600 (Sat, 10 Jan 2009) | 1 line make tests fail if they can't be imported ........ r68514 | benjamin.peterson | 2009-01-10 17:41:59 -0600 (Sat, 10 Jan 2009) | 1 line move seealso to a more appropiate place ........ r68515 | benjamin.peterson | 2009-01-10 17:49:08 -0600 (Sat, 10 Jan 2009) | 1 line macos 9 isn't supported ........ r68534 | gregory.p.smith | 2009-01-11 11:53:33 -0600 (Sun, 11 Jan 2009) | 2 lines correct email address ........ r68535 | gregory.p.smith | 2009-01-11 11:57:54 -0600 (Sun, 11 Jan 2009) | 9 lines Update the documentation for binascii and zlib crc32/adler32 functions to better describe the signed vs unsigned return value behavior on different platforms and versions of python. Mention the workaround to make them all return the same thing by using & 0xffffffff. Fixes issue4903. Also needs to be merged into release26-maint, release30-maint, & py3k. ........ r68536 | benjamin.peterson | 2009-01-11 13:48:15 -0600 (Sun, 11 Jan 2009) | 1 line add email addresses ........ r68552 | vinay.sajip | 2009-01-12 14:36:18 -0600 (Mon, 12 Jan 2009) | 1 line Minor changes/corrections in markup. ........ r68563 | benjamin.peterson | 2009-01-12 19:49:10 -0600 (Mon, 12 Jan 2009) | 1 line small logic correction ........ r68570 | raymond.hettinger | 2009-01-13 03:08:32 -0600 (Tue, 13 Jan 2009) | 5 lines Issue 4922: Incorrect comments for MutableSet.add() and MutableSet.discard(). Needs to be backported to 2.6 and forward ported to 3.0 and 3.1. ........ r68571 | armin.ronacher | 2009-01-13 05:52:23 -0600 (Tue, 13 Jan 2009) | 3 lines ast.literal_eval can properly evaluate complex numbers now. This fixes issue4907. ........ r68572 | andrew.kuchling | 2009-01-13 07:40:54 -0600 (Tue, 13 Jan 2009) | 1 line Note that first coord. is left alone ........ r68575 | thomas.heller | 2009-01-13 11:32:28 -0600 (Tue, 13 Jan 2009) | 1 line Fix refcount leak in error cases. Bug found by coverity. ........ r68582 | georg.brandl | 2009-01-13 16:14:01 -0600 (Tue, 13 Jan 2009) | 2 lines Use assertRaises. ........ r68596 | amaury.forgeotdarc | 2009-01-13 17:39:22 -0600 (Tue, 13 Jan 2009) | 3 lines #1162154: inspect.getmembers() now skips attributes that raise AttributeError, e.g. a __slots__ attribute which has not been set. ........ r68623 | vinay.sajip | 2009-01-15 16:48:13 -0600 (Thu, 15 Jan 2009) | 1 line Made minor changes/corrections in markup. Added a couple of section headings. ........ r68624 | vinay.sajip | 2009-01-15 17:04:47 -0600 (Thu, 15 Jan 2009) | 1 line Minor changes/corrections in markup. ........ r68628 | benjamin.peterson | 2009-01-15 20:55:24 -0600 (Thu, 15 Jan 2009) | 1 line compare with == not is #4946 ........
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.. function:: adler32(data[, value])
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Computes an Adler-32 checksum of *data*. (An Adler-32 checksum is almost as
reliable as a CRC32 but can be computed much more quickly.) The result
is an unsigned 32-bit integer. If *value* is present, it is used as
the starting value of the checksum; otherwise, a default value of 1
is used. Passing in *value* allows computing a running checksum over the
Merged revisions 68450,68480-68481,68493,68495,68501,68512,68514-68515,68534-68536,68552,68563,68570-68572,68575,68582,68596,68623-68624,68628 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r68450 | jeffrey.yasskin | 2009-01-09 10:47:07 -0600 (Fri, 09 Jan 2009) | 3 lines Fix issue 4884, preventing a crash in the socket code when python is compiled with llvm-gcc and run with a glibc <2.10. ........ r68480 | vinay.sajip | 2009-01-10 07:38:04 -0600 (Sat, 10 Jan 2009) | 1 line Minor documentation changes cross-referencing NullHandler to the documentation on configuring logging in a library. ........ r68481 | vinay.sajip | 2009-01-10 07:42:04 -0600 (Sat, 10 Jan 2009) | 1 line Corrected an incorrect self-reference. ........ r68493 | benjamin.peterson | 2009-01-10 11:18:55 -0600 (Sat, 10 Jan 2009) | 1 line rewrite verbose conditionals ........ r68495 | benjamin.peterson | 2009-01-10 11:36:44 -0600 (Sat, 10 Jan 2009) | 1 line tp_iter only exists with Py_TPFLAGS_HAVE_ITER #4901 ........ r68501 | vinay.sajip | 2009-01-10 13:22:57 -0600 (Sat, 10 Jan 2009) | 1 line Corrected minor typo and added .currentmodule directives to fix missing cross-references. ........ r68512 | benjamin.peterson | 2009-01-10 16:42:10 -0600 (Sat, 10 Jan 2009) | 1 line make tests fail if they can't be imported ........ r68514 | benjamin.peterson | 2009-01-10 17:41:59 -0600 (Sat, 10 Jan 2009) | 1 line move seealso to a more appropiate place ........ r68515 | benjamin.peterson | 2009-01-10 17:49:08 -0600 (Sat, 10 Jan 2009) | 1 line macos 9 isn't supported ........ r68534 | gregory.p.smith | 2009-01-11 11:53:33 -0600 (Sun, 11 Jan 2009) | 2 lines correct email address ........ r68535 | gregory.p.smith | 2009-01-11 11:57:54 -0600 (Sun, 11 Jan 2009) | 9 lines Update the documentation for binascii and zlib crc32/adler32 functions to better describe the signed vs unsigned return value behavior on different platforms and versions of python. Mention the workaround to make them all return the same thing by using & 0xffffffff. Fixes issue4903. Also needs to be merged into release26-maint, release30-maint, & py3k. ........ r68536 | benjamin.peterson | 2009-01-11 13:48:15 -0600 (Sun, 11 Jan 2009) | 1 line add email addresses ........ r68552 | vinay.sajip | 2009-01-12 14:36:18 -0600 (Mon, 12 Jan 2009) | 1 line Minor changes/corrections in markup. ........ r68563 | benjamin.peterson | 2009-01-12 19:49:10 -0600 (Mon, 12 Jan 2009) | 1 line small logic correction ........ r68570 | raymond.hettinger | 2009-01-13 03:08:32 -0600 (Tue, 13 Jan 2009) | 5 lines Issue 4922: Incorrect comments for MutableSet.add() and MutableSet.discard(). Needs to be backported to 2.6 and forward ported to 3.0 and 3.1. ........ r68571 | armin.ronacher | 2009-01-13 05:52:23 -0600 (Tue, 13 Jan 2009) | 3 lines ast.literal_eval can properly evaluate complex numbers now. This fixes issue4907. ........ r68572 | andrew.kuchling | 2009-01-13 07:40:54 -0600 (Tue, 13 Jan 2009) | 1 line Note that first coord. is left alone ........ r68575 | thomas.heller | 2009-01-13 11:32:28 -0600 (Tue, 13 Jan 2009) | 1 line Fix refcount leak in error cases. Bug found by coverity. ........ r68582 | georg.brandl | 2009-01-13 16:14:01 -0600 (Tue, 13 Jan 2009) | 2 lines Use assertRaises. ........ r68596 | amaury.forgeotdarc | 2009-01-13 17:39:22 -0600 (Tue, 13 Jan 2009) | 3 lines #1162154: inspect.getmembers() now skips attributes that raise AttributeError, e.g. a __slots__ attribute which has not been set. ........ r68623 | vinay.sajip | 2009-01-15 16:48:13 -0600 (Thu, 15 Jan 2009) | 1 line Made minor changes/corrections in markup. Added a couple of section headings. ........ r68624 | vinay.sajip | 2009-01-15 17:04:47 -0600 (Thu, 15 Jan 2009) | 1 line Minor changes/corrections in markup. ........ r68628 | benjamin.peterson | 2009-01-15 20:55:24 -0600 (Thu, 15 Jan 2009) | 1 line compare with == not is #4946 ........
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concatenation of several inputs. The algorithm is not cryptographically
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strong, and should not be used for authentication or digital signatures. Since
the algorithm is designed for use as a checksum algorithm, it is not suitable
for use as a general hash algorithm.
.. versionchanged:: 3.0
Always returns an unsigned value.
To generate the same numeric value across all Python versions and
platforms, use ``adler32(data) & 0xffffffff``.
Merged revisions 68450,68480-68481,68493,68495,68501,68512,68514-68515,68534-68536,68552,68563,68570-68572,68575,68582,68596,68623-68624,68628 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r68450 | jeffrey.yasskin | 2009-01-09 10:47:07 -0600 (Fri, 09 Jan 2009) | 3 lines Fix issue 4884, preventing a crash in the socket code when python is compiled with llvm-gcc and run with a glibc <2.10. ........ r68480 | vinay.sajip | 2009-01-10 07:38:04 -0600 (Sat, 10 Jan 2009) | 1 line Minor documentation changes cross-referencing NullHandler to the documentation on configuring logging in a library. ........ r68481 | vinay.sajip | 2009-01-10 07:42:04 -0600 (Sat, 10 Jan 2009) | 1 line Corrected an incorrect self-reference. ........ r68493 | benjamin.peterson | 2009-01-10 11:18:55 -0600 (Sat, 10 Jan 2009) | 1 line rewrite verbose conditionals ........ r68495 | benjamin.peterson | 2009-01-10 11:36:44 -0600 (Sat, 10 Jan 2009) | 1 line tp_iter only exists with Py_TPFLAGS_HAVE_ITER #4901 ........ r68501 | vinay.sajip | 2009-01-10 13:22:57 -0600 (Sat, 10 Jan 2009) | 1 line Corrected minor typo and added .currentmodule directives to fix missing cross-references. ........ r68512 | benjamin.peterson | 2009-01-10 16:42:10 -0600 (Sat, 10 Jan 2009) | 1 line make tests fail if they can't be imported ........ r68514 | benjamin.peterson | 2009-01-10 17:41:59 -0600 (Sat, 10 Jan 2009) | 1 line move seealso to a more appropiate place ........ r68515 | benjamin.peterson | 2009-01-10 17:49:08 -0600 (Sat, 10 Jan 2009) | 1 line macos 9 isn't supported ........ r68534 | gregory.p.smith | 2009-01-11 11:53:33 -0600 (Sun, 11 Jan 2009) | 2 lines correct email address ........ r68535 | gregory.p.smith | 2009-01-11 11:57:54 -0600 (Sun, 11 Jan 2009) | 9 lines Update the documentation for binascii and zlib crc32/adler32 functions to better describe the signed vs unsigned return value behavior on different platforms and versions of python. Mention the workaround to make them all return the same thing by using & 0xffffffff. Fixes issue4903. Also needs to be merged into release26-maint, release30-maint, & py3k. ........ r68536 | benjamin.peterson | 2009-01-11 13:48:15 -0600 (Sun, 11 Jan 2009) | 1 line add email addresses ........ r68552 | vinay.sajip | 2009-01-12 14:36:18 -0600 (Mon, 12 Jan 2009) | 1 line Minor changes/corrections in markup. ........ r68563 | benjamin.peterson | 2009-01-12 19:49:10 -0600 (Mon, 12 Jan 2009) | 1 line small logic correction ........ r68570 | raymond.hettinger | 2009-01-13 03:08:32 -0600 (Tue, 13 Jan 2009) | 5 lines Issue 4922: Incorrect comments for MutableSet.add() and MutableSet.discard(). Needs to be backported to 2.6 and forward ported to 3.0 and 3.1. ........ r68571 | armin.ronacher | 2009-01-13 05:52:23 -0600 (Tue, 13 Jan 2009) | 3 lines ast.literal_eval can properly evaluate complex numbers now. This fixes issue4907. ........ r68572 | andrew.kuchling | 2009-01-13 07:40:54 -0600 (Tue, 13 Jan 2009) | 1 line Note that first coord. is left alone ........ r68575 | thomas.heller | 2009-01-13 11:32:28 -0600 (Tue, 13 Jan 2009) | 1 line Fix refcount leak in error cases. Bug found by coverity. ........ r68582 | georg.brandl | 2009-01-13 16:14:01 -0600 (Tue, 13 Jan 2009) | 2 lines Use assertRaises. ........ r68596 | amaury.forgeotdarc | 2009-01-13 17:39:22 -0600 (Tue, 13 Jan 2009) | 3 lines #1162154: inspect.getmembers() now skips attributes that raise AttributeError, e.g. a __slots__ attribute which has not been set. ........ r68623 | vinay.sajip | 2009-01-15 16:48:13 -0600 (Thu, 15 Jan 2009) | 1 line Made minor changes/corrections in markup. Added a couple of section headings. ........ r68624 | vinay.sajip | 2009-01-15 17:04:47 -0600 (Thu, 15 Jan 2009) | 1 line Minor changes/corrections in markup. ........ r68628 | benjamin.peterson | 2009-01-15 20:55:24 -0600 (Thu, 15 Jan 2009) | 1 line compare with == not is #4946 ........
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.. function:: compress(data, level=-1)
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Compresses the bytes in *data*, returning a bytes object containing compressed data.
*level* is an integer from ``0`` to ``9`` or ``-1`` controlling the level of compression;
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``1`` is fastest and produces the least compression, ``9`` is slowest and
produces the most. ``0`` is no compression. The default value is ``-1``
(Z_DEFAULT_COMPRESSION). Z_DEFAULT_COMPRESSION represents a default
compromise between speed and compression (currently equivalent to level 6).
Raises the :exc:`error` exception if any error occurs.
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.. versionchanged:: 3.6
Keyword arguments are now supported.
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.. function:: compressobj(level=-1, method=DEFLATED, wbits=15, memLevel=8, strategy=Z_DEFAULT_STRATEGY[, zdict])
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Returns a compression object, to be used for compressing data streams that won't
fit into memory at once.
*level* is the compression level -- an integer from ``0`` to ``9`` or ``-1``.
A value of ``1`` is fastest and produces the least compression, while a value of
``9`` is slowest and produces the most. ``0`` is no compression. The default
value is ``-1`` (Z_DEFAULT_COMPRESSION). Z_DEFAULT_COMPRESSION represents a default
compromise between speed and compression (currently equivalent to level 6).
*method* is the compression algorithm. Currently, the only supported value is
``DEFLATED``.
*wbits* is the base two logarithm of the size of the window buffer. This
should be an integer from ``8`` to ``15``. Higher values give better
compression, but use more memory.
The *memLevel* argument controls the amount of memory used for the
internal compression state. Valid values range from ``1`` to ``9``.
Higher values use more memory, but are faster and produce smaller output.
*strategy* is used to tune the compression algorithm. Possible values are
``Z_DEFAULT_STRATEGY``, ``Z_FILTERED``, and ``Z_HUFFMAN_ONLY``.
*zdict* is a predefined compression dictionary. This is a sequence of bytes
(such as a :class:`bytes` object) containing subsequences that are expected
to occur frequently in the data that is to be compressed. Those subsequences
that are expected to be most common should come at the end of the dictionary.
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.. versionchanged:: 3.3
Added the *zdict* parameter and keyword argument support.
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Merged revisions 68450,68480-68481,68493,68495,68501,68512,68514-68515,68534-68536,68552,68563,68570-68572,68575,68582,68596,68623-68624,68628 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r68450 | jeffrey.yasskin | 2009-01-09 10:47:07 -0600 (Fri, 09 Jan 2009) | 3 lines Fix issue 4884, preventing a crash in the socket code when python is compiled with llvm-gcc and run with a glibc <2.10. ........ r68480 | vinay.sajip | 2009-01-10 07:38:04 -0600 (Sat, 10 Jan 2009) | 1 line Minor documentation changes cross-referencing NullHandler to the documentation on configuring logging in a library. ........ r68481 | vinay.sajip | 2009-01-10 07:42:04 -0600 (Sat, 10 Jan 2009) | 1 line Corrected an incorrect self-reference. ........ r68493 | benjamin.peterson | 2009-01-10 11:18:55 -0600 (Sat, 10 Jan 2009) | 1 line rewrite verbose conditionals ........ r68495 | benjamin.peterson | 2009-01-10 11:36:44 -0600 (Sat, 10 Jan 2009) | 1 line tp_iter only exists with Py_TPFLAGS_HAVE_ITER #4901 ........ r68501 | vinay.sajip | 2009-01-10 13:22:57 -0600 (Sat, 10 Jan 2009) | 1 line Corrected minor typo and added .currentmodule directives to fix missing cross-references. ........ r68512 | benjamin.peterson | 2009-01-10 16:42:10 -0600 (Sat, 10 Jan 2009) | 1 line make tests fail if they can't be imported ........ r68514 | benjamin.peterson | 2009-01-10 17:41:59 -0600 (Sat, 10 Jan 2009) | 1 line move seealso to a more appropiate place ........ r68515 | benjamin.peterson | 2009-01-10 17:49:08 -0600 (Sat, 10 Jan 2009) | 1 line macos 9 isn't supported ........ r68534 | gregory.p.smith | 2009-01-11 11:53:33 -0600 (Sun, 11 Jan 2009) | 2 lines correct email address ........ r68535 | gregory.p.smith | 2009-01-11 11:57:54 -0600 (Sun, 11 Jan 2009) | 9 lines Update the documentation for binascii and zlib crc32/adler32 functions to better describe the signed vs unsigned return value behavior on different platforms and versions of python. Mention the workaround to make them all return the same thing by using & 0xffffffff. Fixes issue4903. Also needs to be merged into release26-maint, release30-maint, & py3k. ........ r68536 | benjamin.peterson | 2009-01-11 13:48:15 -0600 (Sun, 11 Jan 2009) | 1 line add email addresses ........ r68552 | vinay.sajip | 2009-01-12 14:36:18 -0600 (Mon, 12 Jan 2009) | 1 line Minor changes/corrections in markup. ........ r68563 | benjamin.peterson | 2009-01-12 19:49:10 -0600 (Mon, 12 Jan 2009) | 1 line small logic correction ........ r68570 | raymond.hettinger | 2009-01-13 03:08:32 -0600 (Tue, 13 Jan 2009) | 5 lines Issue 4922: Incorrect comments for MutableSet.add() and MutableSet.discard(). Needs to be backported to 2.6 and forward ported to 3.0 and 3.1. ........ r68571 | armin.ronacher | 2009-01-13 05:52:23 -0600 (Tue, 13 Jan 2009) | 3 lines ast.literal_eval can properly evaluate complex numbers now. This fixes issue4907. ........ r68572 | andrew.kuchling | 2009-01-13 07:40:54 -0600 (Tue, 13 Jan 2009) | 1 line Note that first coord. is left alone ........ r68575 | thomas.heller | 2009-01-13 11:32:28 -0600 (Tue, 13 Jan 2009) | 1 line Fix refcount leak in error cases. Bug found by coverity. ........ r68582 | georg.brandl | 2009-01-13 16:14:01 -0600 (Tue, 13 Jan 2009) | 2 lines Use assertRaises. ........ r68596 | amaury.forgeotdarc | 2009-01-13 17:39:22 -0600 (Tue, 13 Jan 2009) | 3 lines #1162154: inspect.getmembers() now skips attributes that raise AttributeError, e.g. a __slots__ attribute which has not been set. ........ r68623 | vinay.sajip | 2009-01-15 16:48:13 -0600 (Thu, 15 Jan 2009) | 1 line Made minor changes/corrections in markup. Added a couple of section headings. ........ r68624 | vinay.sajip | 2009-01-15 17:04:47 -0600 (Thu, 15 Jan 2009) | 1 line Minor changes/corrections in markup. ........ r68628 | benjamin.peterson | 2009-01-15 20:55:24 -0600 (Thu, 15 Jan 2009) | 1 line compare with == not is #4946 ........
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.. function:: crc32(data[, value])
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.. index::
single: Cyclic Redundancy Check
single: checksum; Cyclic Redundancy Check
Computes a CRC (Cyclic Redundancy Check) checksum of *data*. The
result is an unsigned 32-bit integer. If *value* is present, it is used
as the starting value of the checksum; otherwise, a default value of 0
is used. Passing in *value* allows computing a running checksum over the
Merged revisions 68450,68480-68481,68493,68495,68501,68512,68514-68515,68534-68536,68552,68563,68570-68572,68575,68582,68596,68623-68624,68628 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r68450 | jeffrey.yasskin | 2009-01-09 10:47:07 -0600 (Fri, 09 Jan 2009) | 3 lines Fix issue 4884, preventing a crash in the socket code when python is compiled with llvm-gcc and run with a glibc <2.10. ........ r68480 | vinay.sajip | 2009-01-10 07:38:04 -0600 (Sat, 10 Jan 2009) | 1 line Minor documentation changes cross-referencing NullHandler to the documentation on configuring logging in a library. ........ r68481 | vinay.sajip | 2009-01-10 07:42:04 -0600 (Sat, 10 Jan 2009) | 1 line Corrected an incorrect self-reference. ........ r68493 | benjamin.peterson | 2009-01-10 11:18:55 -0600 (Sat, 10 Jan 2009) | 1 line rewrite verbose conditionals ........ r68495 | benjamin.peterson | 2009-01-10 11:36:44 -0600 (Sat, 10 Jan 2009) | 1 line tp_iter only exists with Py_TPFLAGS_HAVE_ITER #4901 ........ r68501 | vinay.sajip | 2009-01-10 13:22:57 -0600 (Sat, 10 Jan 2009) | 1 line Corrected minor typo and added .currentmodule directives to fix missing cross-references. ........ r68512 | benjamin.peterson | 2009-01-10 16:42:10 -0600 (Sat, 10 Jan 2009) | 1 line make tests fail if they can't be imported ........ r68514 | benjamin.peterson | 2009-01-10 17:41:59 -0600 (Sat, 10 Jan 2009) | 1 line move seealso to a more appropiate place ........ r68515 | benjamin.peterson | 2009-01-10 17:49:08 -0600 (Sat, 10 Jan 2009) | 1 line macos 9 isn't supported ........ r68534 | gregory.p.smith | 2009-01-11 11:53:33 -0600 (Sun, 11 Jan 2009) | 2 lines correct email address ........ r68535 | gregory.p.smith | 2009-01-11 11:57:54 -0600 (Sun, 11 Jan 2009) | 9 lines Update the documentation for binascii and zlib crc32/adler32 functions to better describe the signed vs unsigned return value behavior on different platforms and versions of python. Mention the workaround to make them all return the same thing by using & 0xffffffff. Fixes issue4903. Also needs to be merged into release26-maint, release30-maint, & py3k. ........ r68536 | benjamin.peterson | 2009-01-11 13:48:15 -0600 (Sun, 11 Jan 2009) | 1 line add email addresses ........ r68552 | vinay.sajip | 2009-01-12 14:36:18 -0600 (Mon, 12 Jan 2009) | 1 line Minor changes/corrections in markup. ........ r68563 | benjamin.peterson | 2009-01-12 19:49:10 -0600 (Mon, 12 Jan 2009) | 1 line small logic correction ........ r68570 | raymond.hettinger | 2009-01-13 03:08:32 -0600 (Tue, 13 Jan 2009) | 5 lines Issue 4922: Incorrect comments for MutableSet.add() and MutableSet.discard(). Needs to be backported to 2.6 and forward ported to 3.0 and 3.1. ........ r68571 | armin.ronacher | 2009-01-13 05:52:23 -0600 (Tue, 13 Jan 2009) | 3 lines ast.literal_eval can properly evaluate complex numbers now. This fixes issue4907. ........ r68572 | andrew.kuchling | 2009-01-13 07:40:54 -0600 (Tue, 13 Jan 2009) | 1 line Note that first coord. is left alone ........ r68575 | thomas.heller | 2009-01-13 11:32:28 -0600 (Tue, 13 Jan 2009) | 1 line Fix refcount leak in error cases. Bug found by coverity. ........ r68582 | georg.brandl | 2009-01-13 16:14:01 -0600 (Tue, 13 Jan 2009) | 2 lines Use assertRaises. ........ r68596 | amaury.forgeotdarc | 2009-01-13 17:39:22 -0600 (Tue, 13 Jan 2009) | 3 lines #1162154: inspect.getmembers() now skips attributes that raise AttributeError, e.g. a __slots__ attribute which has not been set. ........ r68623 | vinay.sajip | 2009-01-15 16:48:13 -0600 (Thu, 15 Jan 2009) | 1 line Made minor changes/corrections in markup. Added a couple of section headings. ........ r68624 | vinay.sajip | 2009-01-15 17:04:47 -0600 (Thu, 15 Jan 2009) | 1 line Minor changes/corrections in markup. ........ r68628 | benjamin.peterson | 2009-01-15 20:55:24 -0600 (Thu, 15 Jan 2009) | 1 line compare with == not is #4946 ........
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concatenation of several inputs. The algorithm is not cryptographically
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strong, and should not be used for authentication or digital signatures. Since
the algorithm is designed for use as a checksum algorithm, it is not suitable
for use as a general hash algorithm.
.. versionchanged:: 3.0
Always returns an unsigned value.
To generate the same numeric value across all Python versions and
platforms, use ``crc32(data) & 0xffffffff``.
Merged revisions 68450,68480-68481,68493,68495,68501,68512,68514-68515,68534-68536,68552,68563,68570-68572,68575,68582,68596,68623-68624,68628 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r68450 | jeffrey.yasskin | 2009-01-09 10:47:07 -0600 (Fri, 09 Jan 2009) | 3 lines Fix issue 4884, preventing a crash in the socket code when python is compiled with llvm-gcc and run with a glibc <2.10. ........ r68480 | vinay.sajip | 2009-01-10 07:38:04 -0600 (Sat, 10 Jan 2009) | 1 line Minor documentation changes cross-referencing NullHandler to the documentation on configuring logging in a library. ........ r68481 | vinay.sajip | 2009-01-10 07:42:04 -0600 (Sat, 10 Jan 2009) | 1 line Corrected an incorrect self-reference. ........ r68493 | benjamin.peterson | 2009-01-10 11:18:55 -0600 (Sat, 10 Jan 2009) | 1 line rewrite verbose conditionals ........ r68495 | benjamin.peterson | 2009-01-10 11:36:44 -0600 (Sat, 10 Jan 2009) | 1 line tp_iter only exists with Py_TPFLAGS_HAVE_ITER #4901 ........ r68501 | vinay.sajip | 2009-01-10 13:22:57 -0600 (Sat, 10 Jan 2009) | 1 line Corrected minor typo and added .currentmodule directives to fix missing cross-references. ........ r68512 | benjamin.peterson | 2009-01-10 16:42:10 -0600 (Sat, 10 Jan 2009) | 1 line make tests fail if they can't be imported ........ r68514 | benjamin.peterson | 2009-01-10 17:41:59 -0600 (Sat, 10 Jan 2009) | 1 line move seealso to a more appropiate place ........ r68515 | benjamin.peterson | 2009-01-10 17:49:08 -0600 (Sat, 10 Jan 2009) | 1 line macos 9 isn't supported ........ r68534 | gregory.p.smith | 2009-01-11 11:53:33 -0600 (Sun, 11 Jan 2009) | 2 lines correct email address ........ r68535 | gregory.p.smith | 2009-01-11 11:57:54 -0600 (Sun, 11 Jan 2009) | 9 lines Update the documentation for binascii and zlib crc32/adler32 functions to better describe the signed vs unsigned return value behavior on different platforms and versions of python. Mention the workaround to make them all return the same thing by using & 0xffffffff. Fixes issue4903. Also needs to be merged into release26-maint, release30-maint, & py3k. ........ r68536 | benjamin.peterson | 2009-01-11 13:48:15 -0600 (Sun, 11 Jan 2009) | 1 line add email addresses ........ r68552 | vinay.sajip | 2009-01-12 14:36:18 -0600 (Mon, 12 Jan 2009) | 1 line Minor changes/corrections in markup. ........ r68563 | benjamin.peterson | 2009-01-12 19:49:10 -0600 (Mon, 12 Jan 2009) | 1 line small logic correction ........ r68570 | raymond.hettinger | 2009-01-13 03:08:32 -0600 (Tue, 13 Jan 2009) | 5 lines Issue 4922: Incorrect comments for MutableSet.add() and MutableSet.discard(). Needs to be backported to 2.6 and forward ported to 3.0 and 3.1. ........ r68571 | armin.ronacher | 2009-01-13 05:52:23 -0600 (Tue, 13 Jan 2009) | 3 lines ast.literal_eval can properly evaluate complex numbers now. This fixes issue4907. ........ r68572 | andrew.kuchling | 2009-01-13 07:40:54 -0600 (Tue, 13 Jan 2009) | 1 line Note that first coord. is left alone ........ r68575 | thomas.heller | 2009-01-13 11:32:28 -0600 (Tue, 13 Jan 2009) | 1 line Fix refcount leak in error cases. Bug found by coverity. ........ r68582 | georg.brandl | 2009-01-13 16:14:01 -0600 (Tue, 13 Jan 2009) | 2 lines Use assertRaises. ........ r68596 | amaury.forgeotdarc | 2009-01-13 17:39:22 -0600 (Tue, 13 Jan 2009) | 3 lines #1162154: inspect.getmembers() now skips attributes that raise AttributeError, e.g. a __slots__ attribute which has not been set. ........ r68623 | vinay.sajip | 2009-01-15 16:48:13 -0600 (Thu, 15 Jan 2009) | 1 line Made minor changes/corrections in markup. Added a couple of section headings. ........ r68624 | vinay.sajip | 2009-01-15 17:04:47 -0600 (Thu, 15 Jan 2009) | 1 line Minor changes/corrections in markup. ........ r68628 | benjamin.peterson | 2009-01-15 20:55:24 -0600 (Thu, 15 Jan 2009) | 1 line compare with == not is #4946 ........
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.. function:: decompress(data[, wbits[, bufsize]])
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Decompresses the bytes in *data*, returning a bytes object containing the
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uncompressed data. The *wbits* parameter controls the size of the window
Merged revisions 78338,78345-78346,78561-78562,78566,78574,78581,78634,78660,78675 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r78338 | andrew.kuchling | 2010-02-22 15:04:02 -0600 (Mon, 22 Feb 2010) | 4 lines Remove Tools/modulator, a reference to it in the docs, and a screenshot of it. (I asked the BDFL first, and he approved removing it. The last actual bugfix to Tools/modulator was in 2001; since then all changes have been search-and-replace: string methods, whitespace fixes, etc.) ........ r78345 | andrew.kuchling | 2010-02-22 17:10:52 -0600 (Mon, 22 Feb 2010) | 1 line #7706: DONT_HAVE_ERRNO_H is no longer defined by configure (after rev.46819). ........ r78346 | andrew.kuchling | 2010-02-22 17:12:00 -0600 (Mon, 22 Feb 2010) | 1 line #7706: add include guards where they're missing; required for Windows CE ........ r78561 | andrew.kuchling | 2010-03-01 13:51:43 -0600 (Mon, 01 Mar 2010) | 1 line #7191: describe more details of wbits parameter ........ r78562 | andrew.kuchling | 2010-03-01 14:11:57 -0600 (Mon, 01 Mar 2010) | 1 line #7637: avoid repeated-concatenation antipattern in example ........ r78566 | barry.warsaw | 2010-03-01 15:46:51 -0600 (Mon, 01 Mar 2010) | 4 lines Manually copy patch for bug 7250 from the release26-maint branch. I suck because I did this in the wrong order and couldn't smack svnmerge into submission. ........ r78574 | benjamin.peterson | 2010-03-01 17:25:13 -0600 (Mon, 01 Mar 2010) | 1 line remove CVS id ........ r78581 | michael.foord | 2010-03-02 08:22:15 -0600 (Tue, 02 Mar 2010) | 1 line Link correction in documentation. ........ r78634 | benjamin.peterson | 2010-03-03 15:28:25 -0600 (Wed, 03 Mar 2010) | 1 line rephrase ........ r78660 | dirkjan.ochtman | 2010-03-04 13:21:53 -0600 (Thu, 04 Mar 2010) | 4 lines Try to fix buildbot breakage from r78384. Thanks bitdancer and briancurtin for the help. ........ r78675 | florent.xicluna | 2010-03-04 19:12:14 -0600 (Thu, 04 Mar 2010) | 2 lines These line should not be there. ........
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buffer, and is discussed further below.
If *bufsize* is given, it is used as the initial size of the output
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buffer. Raises the :exc:`error` exception if any error occurs.
The absolute value of *wbits* is the base two logarithm of the size of the
history buffer (the "window size") used when compressing data. Its absolute
value should be between 8 and 15 for the most recent versions of the zlib
library, larger values resulting in better compression at the expense of greater
Merged revisions 78338,78345-78346,78561-78562,78566,78574,78581,78634,78660,78675 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r78338 | andrew.kuchling | 2010-02-22 15:04:02 -0600 (Mon, 22 Feb 2010) | 4 lines Remove Tools/modulator, a reference to it in the docs, and a screenshot of it. (I asked the BDFL first, and he approved removing it. The last actual bugfix to Tools/modulator was in 2001; since then all changes have been search-and-replace: string methods, whitespace fixes, etc.) ........ r78345 | andrew.kuchling | 2010-02-22 17:10:52 -0600 (Mon, 22 Feb 2010) | 1 line #7706: DONT_HAVE_ERRNO_H is no longer defined by configure (after rev.46819). ........ r78346 | andrew.kuchling | 2010-02-22 17:12:00 -0600 (Mon, 22 Feb 2010) | 1 line #7706: add include guards where they're missing; required for Windows CE ........ r78561 | andrew.kuchling | 2010-03-01 13:51:43 -0600 (Mon, 01 Mar 2010) | 1 line #7191: describe more details of wbits parameter ........ r78562 | andrew.kuchling | 2010-03-01 14:11:57 -0600 (Mon, 01 Mar 2010) | 1 line #7637: avoid repeated-concatenation antipattern in example ........ r78566 | barry.warsaw | 2010-03-01 15:46:51 -0600 (Mon, 01 Mar 2010) | 4 lines Manually copy patch for bug 7250 from the release26-maint branch. I suck because I did this in the wrong order and couldn't smack svnmerge into submission. ........ r78574 | benjamin.peterson | 2010-03-01 17:25:13 -0600 (Mon, 01 Mar 2010) | 1 line remove CVS id ........ r78581 | michael.foord | 2010-03-02 08:22:15 -0600 (Tue, 02 Mar 2010) | 1 line Link correction in documentation. ........ r78634 | benjamin.peterson | 2010-03-03 15:28:25 -0600 (Wed, 03 Mar 2010) | 1 line rephrase ........ r78660 | dirkjan.ochtman | 2010-03-04 13:21:53 -0600 (Thu, 04 Mar 2010) | 4 lines Try to fix buildbot breakage from r78384. Thanks bitdancer and briancurtin for the help. ........ r78675 | florent.xicluna | 2010-03-04 19:12:14 -0600 (Thu, 04 Mar 2010) | 2 lines These line should not be there. ........
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memory usage. When decompressing a stream, *wbits* must not be smaller
than the size originally used to compress the stream; using a too-small
value will result in an exception. The default value is therefore the
highest value, 15. When *wbits* is negative, the standard
:program:`gzip` header is suppressed.
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*bufsize* is the initial size of the buffer used to hold decompressed data. If
more space is required, the buffer size will be increased as needed, so you
don't have to get this value exactly right; tuning it will only save a few calls
to :c:func:`malloc`. The default size is 16384.
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.. function:: decompressobj(wbits=15[, zdict])
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Returns a decompression object, to be used for decompressing data streams that
won't fit into memory at once.
The *wbits* parameter controls the size of the window buffer.
The *zdict* parameter specifies a predefined compression dictionary. If
provided, this must be the same dictionary as was used by the compressor that
produced the data that is to be decompressed.
.. note::
If *zdict* is a mutable object (such as a :class:`bytearray`), you must not
modify its contents between the call to :func:`decompressobj` and the first
call to the decompressor's ``decompress()`` method.
.. versionchanged:: 3.3
Added the *zdict* parameter.
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Compression objects support the following methods:
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.. method:: Compress.compress(data)
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Compress *data*, returning a bytes object containing compressed data for at least
part of the data in *data*. This data should be concatenated to the output
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produced by any preceding calls to the :meth:`compress` method. Some input may
be kept in internal buffers for later processing.
.. method:: Compress.flush([mode])
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All pending input is processed, and a bytes object containing the remaining compressed
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output is returned. *mode* can be selected from the constants
:const:`Z_SYNC_FLUSH`, :const:`Z_FULL_FLUSH`, or :const:`Z_FINISH`,
defaulting to :const:`Z_FINISH`. :const:`Z_SYNC_FLUSH` and
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:const:`Z_FULL_FLUSH` allow compressing further bytestrings of data, while
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:const:`Z_FINISH` finishes the compressed stream and prevents compressing any
more data. After calling :meth:`flush` with *mode* set to :const:`Z_FINISH`,
the :meth:`compress` method cannot be called again; the only realistic action is
to delete the object.
.. method:: Compress.copy()
Returns a copy of the compression object. This can be used to efficiently
compress a set of data that share a common initial prefix.
Decompression objects support the following methods and attributes:
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.. attribute:: Decompress.unused_data
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A bytes object which contains any bytes past the end of the compressed data. That is,
this remains ``b""`` until the last byte that contains compression data is
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available. If the whole bytestring turned out to contain compressed data, this is
``b""``, an empty bytes object.
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.. attribute:: Decompress.unconsumed_tail
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A bytes object that contains any data that was not consumed by the last
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:meth:`decompress` call because it exceeded the limit for the uncompressed data
buffer. This data has not yet been seen by the zlib machinery, so you must feed
it (possibly with further data concatenated to it) back to a subsequent
:meth:`decompress` method call in order to get correct output.
.. attribute:: Decompress.eof
A boolean indicating whether the end of the compressed data stream has been
reached.
This makes it possible to distinguish between a properly-formed compressed
stream, and an incomplete or truncated one.
.. versionadded:: 3.3
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.. method:: Decompress.decompress(data[, max_length])
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Decompress *data*, returning a bytes object containing the uncompressed data
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corresponding to at least part of the data in *string*. This data should be
concatenated to the output produced by any preceding calls to the
:meth:`decompress` method. Some of the input data may be preserved in internal
buffers for later processing.
If the optional parameter *max_length* is non-zero then the return value will be
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no longer than *max_length*. This may mean that not all of the compressed input
can be processed; and unconsumed data will be stored in the attribute
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:attr:`unconsumed_tail`. This bytestring must be passed to a subsequent call to
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:meth:`decompress` if decompression is to continue. If *max_length* is not
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supplied then the whole input is decompressed, and :attr:`unconsumed_tail` is
empty.
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.. method:: Decompress.flush([length])
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All pending input is processed, and a bytes object containing the remaining
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uncompressed output is returned. After calling :meth:`flush`, the
:meth:`decompress` method cannot be called again; the only realistic action is
to delete the object.
The optional parameter *length* sets the initial size of the output buffer.
.. method:: Decompress.copy()
Returns a copy of the decompression object. This can be used to save the state
of the decompressor midway through the data stream in order to speed up random
seeks into the stream at a future point.
Information about the version of the zlib library in use is available through
the following constants:
.. data:: ZLIB_VERSION
The version string of the zlib library that was used for building the module.
This may be different from the zlib library actually used at runtime, which
is available as :const:`ZLIB_RUNTIME_VERSION`.
.. data:: ZLIB_RUNTIME_VERSION
The version string of the zlib library actually loaded by the interpreter.
.. versionadded:: 3.3
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.. seealso::
Module :mod:`gzip`
Reading and writing :program:`gzip`\ -format files.
http://www.zlib.net
The zlib library home page.
http://www.zlib.net/manual.html
The zlib manual explains the semantics and usage of the library's many
functions.