:mod:`gzip` --- Support for :program:`gzip` files

Source code: :source:`Lib/gzip.py`

---

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

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

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

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

The module defines the following items:

Constructor for the :class:`GzipFile` class, which simulates most of the methods of a :term:`file object`, with the exception of the :meth:`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 :class:`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 :program:`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 :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 mtime argument is an optional numeric timestamp to be written to the stream when compressing. All :program:`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 :program:`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 :class:`GzipFile` object's :meth:`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 :class:`io.BytesIO` object opened for writing as fileobj, and retrieve the resulting memory buffer using the :class:`io.BytesIO` object's :meth:`~io.BytesIO.getvalue` method.

:class:`GzipFile` supports the :class:`io.BufferedIOBase` interface, including iteration and the :keyword:`with` statement. Only the :meth:`read1` and :meth:`truncate` methods aren't implemented.

:class:`GzipFile` also provides the following method:

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)