Issue #15677: Document that zlib and gzip accept a compression level of 0 to mean 'no compression'.

Patch by Brian Brazil.

Doc/library/gzip.rst

@@ -49,9 +49,10 @@ The module defines the following items:
    not given, the 'b' flag will be added to the mode to ensure the file is opened
    in binary mode for cross-platform portability.
 
-   The *compresslevel* argument is an integer from ``1`` to ``9`` controlling the
-   level of compression; ``1`` is fastest and produces the least compression, and
-   ``9`` is slowest and produces the most compression.  The default is ``9``.
+   The *compresslevel* argument is an integer from ``0`` to ``9`` controlling
+   the level of compression; ``1`` is fastest and produces the least
+   compression, and ``9`` is slowest and produces the most compression. ``0``
+   is no compression. The default is ``9``.
 
    The *mtime* argument is an optional numeric timestamp to be written to
    the stream when compressing.  All :program:`gzip` compressed streams are

Doc/library/zlib.rst

@@ -62,18 +62,19 @@ The available exception and functions in this module are:
 .. function:: compress(string[, level])
 
    Compresses the data in *string*, returning a string contained compressed data.
-   *level* is an integer from ``1`` to ``9`` controlling the level of compression;
+   *level* is an integer from ``0`` to ``9`` controlling the level of compression;
    ``1`` is fastest and produces the least compression, ``9`` is slowest and
-   produces the most.  The default value is ``6``.  Raises the :exc:`error`
-   exception if any error occurs.
+   produces the most.  ``0`` is no compression.  The default value is ``6``.
+   Raises the :exc:`error` exception if any error occurs.
 
 
 .. function:: compressobj([level])
 
    Returns a compression object, to be used for compressing data streams that won't
-   fit into memory at once.  *level* is an integer from ``1`` to ``9`` controlling
+   fit into memory at once.  *level* is an integer from ``0`` to ``9`` controlling
    the level of compression; ``1`` is fastest and produces the least compression,
-   ``9`` is slowest and produces the most.  The default value is ``6``.
+   ``9`` is slowest and produces the most.  ``0`` is no compression.  The default
+   value is ``6``.
 
 
 .. function:: crc32(data[, value])

Lib/gzip.py

@@ -66,9 +66,10 @@ class GzipFile(io.BufferedIOBase):
         Be aware that only the 'rb', 'ab', and 'wb' values should be used
         for cross-platform portability.
 
-        The compresslevel argument is an integer from 1 to 9 controlling the
+        The compresslevel argument is an integer from 0 to 9 controlling the
         level of compression; 1 is fastest and produces the least compression,
-        and 9 is slowest and produces the most compression.  The default is 9.
+        and 9 is slowest and produces the most compression. 0 is no compression
+        at all. The default is 9.
 
         The mtime argument is an optional numeric timestamp to be written
         to the stream when compressing.  All gzip compressed streams

Misc/ACKS

@@ -120,6 +120,7 @@ Monty Brandenberg
 Georg Brandl
 Christopher Brannon
 Terrence Brannon
+Brian Brazil
 Dave Brennan
 Tom Bridgman
 Keith Briggs

Misc/NEWS

@@ -556,6 +556,9 @@ Tools/Demos
 Documentation
 -------------
 
+- Issue #15677: Document that zlib and gzip accept a compression level of 0 to
+  mean 'no compression'. Patch by Brian Brazil.
+
 - Issue #8040: added a version switcher to the documentation.  Patch by
   Yury Selivanov.