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

.. module:: gzip :synopsis: Interfaces for gzip compression and decompression using file objects.

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, as well as the :func:.open, :func:compress and :func:decompress convenience functions. 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:

.. function:: open(filename, mode='rb', compresslevel=9, encoding=None, errors=None, newline=None)

Open a gzip-compressed file in binary or text mode, returning a :term:file object.

The filename argument can be an actual filename (a :class:str or :class:bytes object), or an existing file object to read from or write to.

The mode argument can be any of 'r', 'rb', 'a', 'ab', 'w', 'wb', 'x' or 'xb' for binary mode, or 'rt', 'at', 'wt', or 'xt' for text mode. The default is 'rb'.

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 constructor: GzipFile(filename, mode, compresslevel). In this case, the encoding, errors and newline arguments must not be provided.

For text mode, a :class:GzipFile object is created, and wrapped in an :class:io.TextIOWrapper instance with the specified encoding, error handling behavior, and line ending(s).

.. versionchanged:: 3.3 Added support for filename being a file object, support for text mode, and the encoding, errors and newline arguments.

.. versionchanged:: 3.4 Added support for the 'x', 'xb' and 'xt' modes.

.. versionchanged:: 3.6 Accepts a :term:path-like object.

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

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, an :class:io.BytesIO 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 include 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', 'wb', 'x', or 'xb', 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. To open a compressed file in text mode, use :func:.open (or wrap your :class:GzipFile with an :class: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 last modification time field in the stream when compressing. It should only be provided in compression mode. If omitted or None, the current time is used. See the :attr:mtime attribute for more details.

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 an :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:truncate method isn't implemented.

:class:GzipFile also provides the following method and attribute:

.. 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.

  .. note:: While calling :meth:`peek` does not change the file position of
     the :class:`GzipFile`, it may change the position of the underlying
     file object (e.g. if the :class:`GzipFile` was constructed with the
     *fileobj* parameter).

  .. versionadded:: 3.2

.. attribute:: mtime

  When decompressing, the value of the last modification time field in
  the most recently read header may be read from this attribute, as an
  integer.  The initial value before reading any headers is ``None``.

  All :program:`gzip` compressed streams are required to contain this
  timestamp field.  Some programs, such as :program:`gunzip`\ , make use
  of the timestamp.  The format is the same as the return value of
  :func:`time.time` and the :attr:`~os.stat_result.st_mtime` attribute of
  the object returned by :func:`os.stat`.

.. versionchanged:: 3.1 Support for the :keyword:with statement was added, along with the mtime constructor argument and :attr:mtime attribute.

.. versionchanged:: 3.2 Support for zero-padded and unseekable files was added.

.. versionchanged:: 3.3 The :meth:io.BufferedIOBase.read1 method is now implemented.

.. versionchanged:: 3.4 Added support for the 'x' and 'xb' modes.

.. versionchanged:: 3.5 Added support for writing arbitrary :term:bytes-like objects <bytes-like object>. The :meth:~io.BufferedIOBase.read method now accepts an argument of None.

.. versionchanged:: 3.6 Accepts a :term:path-like object.

.. function:: compress(data, compresslevel=9)

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

.. versionadded:: 3.2

.. function:: decompress(data)

Decompress the data, returning a :class:bytes object containing the uncompressed data.

.. versionadded:: 3.2

.. _gzip-usage-examples:

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

Example of how to GZIP compress a binary string::

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

.. seealso::

Module :mod:zlib The basic data compression module needed to support the :program:gzip file format.