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zlib.rst: Link to constants and deduplicate text #140115

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StanFromIreland Oct 14, 2025
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StanFromIreland Oct 14, 2025
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34 changes: 16 additions & 18 deletions Doc/library/zlib.rst
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Expand Up @@ -58,21 +58,20 @@ The available exception and functions in this module are:

.. versionadded:: next

.. function:: compress(data, /, level=-1, wbits=MAX_WBITS)
.. function:: compress(data, /, level=Z_DEFAULT_COMPRESSION, wbits=MAX_WBITS)
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Per the clinic, this is what it defaults to. Ditto below.


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;
``1`` (Z_BEST_SPEED) is fastest and produces the least compression, ``9`` (Z_BEST_COMPRESSION)
is slowest and produces the most. ``0`` (Z_NO_COMPRESSION) 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).
See :const:`Z_BEST_SPEED` (``1``), :const:`Z_BEST_COMPRESSION` (``9``),
:const:`Z_NO_COMPRESSION` (``0``), and the default,
:const:`Z_DEFAULT_COMPRESSION` (``-1``) for more information about these values.

.. _compress-wbits:

The *wbits* argument controls the size of the history buffer (or the
"window size") used when compressing data, and whether a header and
trailer is included in the output. It can take several ranges of values,
defaulting to ``15`` (MAX_WBITS):
defaulting to ``15`` (:const:`MAX_WBITS`):

* +9 to +15: The base-two logarithm of the window size, which
therefore ranges between 512 and 32768. Larger values produce
Expand All @@ -96,17 +95,15 @@ The available exception and functions in this module are:
The *wbits* parameter is now available to set window bits and
compression type.

.. function:: compressobj(level=-1, method=DEFLATED, wbits=MAX_WBITS, memLevel=DEF_MEM_LEVEL, strategy=Z_DEFAULT_STRATEGY[, zdict])
.. function:: compressobj(level=Z_DEFAULT_COMPRESSION, method=DEFLATED, wbits=MAX_WBITS, memLevel=DEF_MEM_LEVEL, strategy=Z_DEFAULT_STRATEGY[, zdict])

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`` (Z_BEST_SPEED) is fastest and produces the least compression,
while a value of ``9`` (Z_BEST_COMPRESSION) is slowest and produces the most.
``0`` (Z_NO_COMPRESSION) 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).
See :const:`Z_BEST_SPEED` (``1``), :const:`Z_BEST_COMPRESSION` (``9``),
:const:`Z_NO_COMPRESSION` (``0``), and the default,
:const:`Z_DEFAULT_COMPRESSION` (``-1``) for more information about these values.

*method* is the compression algorithm. Currently, the only supported value is
:const:`DEFLATED`.
Expand All @@ -121,7 +118,7 @@ The available exception and functions in this module are:

*strategy* is used to tune the compression algorithm. Possible values are
:const:`Z_DEFAULT_STRATEGY`, :const:`Z_FILTERED`, :const:`Z_HUFFMAN_ONLY`,
:const:`Z_RLE` (zlib 1.2.0.1) and :const:`Z_FIXED` (zlib 1.2.2.2).
:const:`Z_RLE` and :const:`Z_FIXED`.
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I think there is no need to reference version here, the information is now provided in the doc of the constant.


*zdict* is a predefined compression dictionary. This is a sequence of bytes
(such as a :class:`bytes` object) containing subsequences that are expected
Expand Down Expand Up @@ -249,7 +246,7 @@ Compression objects support the following methods:
All pending input is processed, and a bytes object containing the remaining compressed
output is returned. *mode* can be selected from the constants
:const:`Z_NO_FLUSH`, :const:`Z_PARTIAL_FLUSH`, :const:`Z_SYNC_FLUSH`,
:const:`Z_FULL_FLUSH`, :const:`Z_BLOCK` (zlib 1.2.3.4), or :const:`Z_FINISH`,
:const:`Z_FULL_FLUSH`, :const:`Z_BLOCK`, or :const:`Z_FINISH`,
defaulting to :const:`Z_FINISH`. Except :const:`Z_FINISH`, all constants
allow compressing further bytestrings of data, while :const:`Z_FINISH` finishes the
compressed stream and prevents compressing any more data. After calling :meth:`flush`
Expand Down Expand Up @@ -367,24 +364,25 @@ behavior:

.. data:: Z_NO_COMPRESSION

Compression level ``0``.
Compression level ``0``; no compression.

.. versionadded:: 3.6


.. data:: Z_BEST_SPEED

Compression level ``1``.
Compression level ``1``; fastest and produces the least compression.


.. data:: Z_BEST_COMPRESSION

Compression level ``9``.
Compression level ``9``; slowest and produces the most compression.


.. data:: Z_DEFAULT_COMPRESSION

Default compression level (``-1``).
Default compression level (``-1``); a compromise between speed and
compression. Currently equivalent to compression level ``6``.


.. data:: Z_DEFAULT_STRATEGY
Expand Down
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