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

Patch by Brian Brazil.

2 files changed, 11 insertions, 9 deletions

diff --git a/Doc/library/gzip.rst b/Doc/library/gzip.rst
index 50d0462..2cbd2d5 100644
--- a/Doc/library/gzip.rst
+++ b/Doc/library/gzip.rst
@@ -38,7 +38,7 @@ The module defines the following items:
    ``'w'``, or ``'wb'`` for binary mode, or ``'rt'``, ``'at'``, or ``'wt'`` for
    text mode. The default is ``'rb'``.
 
-   The *compresslevel* argument is an integer from 1 to 9, as for the
+   The *compresslevel* argument is an integer from 0 to 9, as for the
    :class:`GzipFile` constructor.
 
    For binary mode, this function is equivalent to the :class:`GzipFile`
@@ -80,9 +80,10 @@ The module defines the following items:
    in text mode, use :func:`.open` (or wrap your :class:`GzipFile` with an
    :class:`io.TextIOWrapper`).
 
-   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
diff --git a/Doc/library/zlib.rst b/Doc/library/zlib.rst
index 42535a0..731023e 100644
--- a/Doc/library/zlib.rst
+++ b/Doc/library/zlib.rst
@@ -52,10 +52,10 @@ The available exception and functions in this module are:
 .. function:: compress(data[, level])
 
    Compresses the bytes in *data*, returning a bytes object containing 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=-1, method=DEFLATED, wbits=15, memlevel=8, strategy=Z_DEFAULT_STRATEGY[, zdict])
@@ -63,9 +63,10 @@ The available exception and functions in this module are:
    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 ``1`` to ``9``. A value
+   *level* is the compression level -- an integer from ``0`` to ``9``. A value
    of ``1`` is fastest and produces the least compression, while a value of
-   ``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``.
 
    *method* is the compression algorithm. Currently, the only supported value is
    ``DEFLATED``.