
``gzip`` --- Support for **gzip** files
***************************************

**Source code:** Lib/gzip.py

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

This module provides a simple interface to compress and decompress
files just like the GNU programs **gzip** and **gunzip** would.

The data compression is provided by the ``zlib`` module.

The ``gzip`` module provides the ``GzipFile`` class. The ``GzipFile``
class reads and writes **gzip**-format files, automatically
compressing or decompressing the data so that it looks like an
ordinary *file object*.

Note that additional file formats which can be decompressed by the
**gzip** and **gunzip** programs, such  as those produced by
**compress** and **pack**, are not supported by this module.

The module defines the following items:

class class gzip.GzipFile(filename=None, mode=None, compresslevel=9, fileobj=None, mtime=None)

   Constructor for the ``GzipFile`` class, which simulates most of the
   methods of a *file object*, with the exception of the
   ``truncate()`` method.  At least one of *fileobj* and *filename*
   must be given a non-trivial value.

   The new class instance is based on *fileobj*, which can be a
   regular file, a ``StringIO`` object, or any other object which
   simulates a file.  It defaults to ``None``, in which case
   *filename* is opened to provide a file object.

   When *fileobj* is not ``None``, the *filename* argument is only
   used to be included in the **gzip** file header, which may includes
   the original filename of the uncompressed file.  It defaults to the
   filename of *fileobj*, if discernible; otherwise, it defaults to
   the empty string, and in this case the original filename is not
   included in the header.

   The *mode* argument can be any of ``'r'``, ``'rb'``, ``'a'``,
   ``'ab'``, ``'w'``, or ``'wb'``, depending on whether the file will
   be read or written.  The default is the mode of *fileobj* if
   discernible; otherwise, the default is ``'rb'``.

   Note that the file is always opened in binary mode; text mode is
   not supported. If you need to read a compressed file in text mode,
   wrap your ``GzipFile`` with an ``io.TextIOWrapper``.

   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 **gzip** compressed streams
   are required to contain a timestamp.  If omitted or ``None``, the
   current time is used.  This module ignores the timestamp when
   decompressing; however, some programs, such as **gunzip**, make use
   of it. The format of the timestamp is the same as that of the
   return value of ``time.time()`` and of the ``st_mtime`` attribute
   of the object returned by ``os.stat()``.

   Calling a ``GzipFile`` object's ``close()`` method does not close
   *fileobj*, since you might wish to append more material after the
   compressed data.  This also allows you to pass a ``io.BytesIO``
   object opened for writing as *fileobj*, and retrieve the resulting
   memory buffer using the ``io.BytesIO`` object's ``getvalue()``
   method.

   ``GzipFile`` supports the ``io.BufferedIOBase`` interface,
   including iteration and the ``with`` statement.  Only the
   ``read1()`` and ``truncate()`` methods aren't implemented.

   ``GzipFile`` also provides the following method:

   peek([n])

      Read *n* uncompressed bytes without advancing the file position.
      At most one single read on the compressed stream is done to
      satisfy the call.  The number of bytes returned may be more or
      less than requested.

      New in version 3.2.

   Changed in version 3.1: Support for the ``with`` statement was
   added.

   Changed in version 3.2: Support for zero-padded files was added.

   Changed in version 3.2: Support for unseekable files was added.

gzip.open(filename, mode='rb', compresslevel=9)

   This is a shorthand for ``GzipFile(filename,`` ``mode,``
   ``compresslevel)``. The *filename* argument is required; *mode*
   defaults to ``'rb'`` and *compresslevel* defaults to ``9``.

gzip.compress(data, compresslevel=9)

   Compress the *data*, returning a ``bytes`` object containing the
   compressed data.  *compresslevel* has the same meaning as in the
   ``GzipFile`` constructor above.

   New in version 3.2.

gzip.decompress(data)

   Decompress the *data*, returning a ``bytes`` object containing the
   uncompressed data.

   New in version 3.2.


Examples of usage
=================

Example of how to read a compressed file:

   import gzip
   with gzip.open('/home/joe/file.txt.gz', 'rb') as f:
       file_content = f.read()

Example of how to create a compressed GZIP file:

   import gzip
   content = b"Lots of content here"
   with gzip.open('/home/joe/file.txt.gz', 'wb') as f:
       f.write(content)

Example of how to GZIP compress an existing file:

   import gzip
   with open('/home/joe/file.txt', 'rb') as f_in:
       with gzip.open('/home/joe/file.txt.gz', 'wb') as f_out:
           f_out.writelines(f_in)

Example of how to GZIP compress a binary string:

   import gzip
   s_in = b"Lots of content here"
   s_out = gzip.compress(s_in)

See also:

   Module ``zlib``
      The basic data compression module needed to support the **gzip**
      file format.
