: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.

.. include:: ../includes/optional-module.rst

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=6, 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.

.. versionchanged:: 3.15 The default compression level was reduced to 6 (down from 9). It is the default level used by most compression tools and a better tradeoff between speed and performance.

.. exception:: BadGzipFile

An exception raised for invalid gzip files. It inherits from :exc:OSError. :exc:EOFError and :exc:zlib.error can also be raised for invalid gzip files.

.. versionadded:: 3.8

.. class:: GzipFile(filename=None, mode=None, compresslevel=6, 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:~io.IOBase.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'. In future Python releases the mode of fileobj will not be used. It is better to always specify mode for writing.

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 optional mtime argument is the timestamp requested by gzip. The time is in Unix format, i.e., seconds since 00:00:00 UTC, January 1, 1970. If mtime is omitted or None, the current time is used. Use mtime = 0 to generate a compressed stream that does not depend on creation time.

See below for the :attr:mtime attribute that is set when decompressing.

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:~io.IOBase.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.
  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:: mode

  ``'rb'`` for reading and ``'wb'`` for writing.

  .. versionchanged:: 3.13
     In previous versions it was an integer ``1`` or ``2``.

.. attribute:: mtime

  When decompressing, this attribute is set to the last timestamp in the most
  recently read header.  It is an integer, holding the number of seconds
  since the Unix epoch (00:00:00 UTC, January 1, 1970).
  The initial value before reading any headers is ``None``.

.. attribute:: name

  The path to the gzip file on disk, as a :class:`str` or :class:`bytes`.
  Equivalent to the output of :func:`os.fspath` on the original input path,
  with no other normalization, resolution or expansion.

.. 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.

.. deprecated:: 3.9 Opening :class:GzipFile for writing without specifying the mode argument is deprecated.

.. versionchanged:: 3.12 Remove the filename attribute, use the :attr:~GzipFile.name attribute instead.

.. versionchanged:: 3.15 The default compression level was reduced to 6 (down from 9). It is the default level used by most compression tools and a better tradeoff between speed and performance.

.. function:: compress(data, compresslevel=6, *, mtime=0)

Compress the data, returning a :class:bytes object containing the compressed data. compresslevel and mtime have the same meaning as in the :class:GzipFile constructor above, but mtime defaults to 0 for reproducible output.

.. versionadded:: 3.2 .. versionchanged:: 3.8 Added the mtime parameter for reproducible output. .. versionchanged:: 3.11 Speed is improved by compressing all data at once instead of in a streamed fashion. Calls with mtime set to 0 are delegated to :func:zlib.compress for better speed. In this situation the output may contain a gzip header "OS" byte value other than 255 "unknown" as supplied by the underlying zlib implementation.

.. versionchanged:: 3.13 The gzip header OS byte is guaranteed to be set to 255 when this function is used as was the case in 3.10 and earlier. .. versionchanged:: 3.14 The mtime parameter now defaults to 0 for reproducible output. For the previous behaviour of using the current time, pass None to mtime. .. versionchanged:: 3.15 The default compression level was reduced to 6 (down from 9). It is the default level used by most compression tools and a better tradeoff between speed and performance.

.. function:: decompress(data)

Decompress the data, returning a :class:bytes object containing the uncompressed data. This function is capable of decompressing multi-member gzip data (multiple gzip blocks concatenated together). When the data is certain to contain only one member the :func:zlib.decompress function with wbits set to 31 is faster.

.. versionadded:: 3.2 .. versionchanged:: 3.11 Speed is improved by decompressing members at once in memory instead of in a streamed fashion.

.. _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.

In case gzip (de)compression is a bottleneck, the python-isal_ package speeds up (de)compression with a mostly compatible API.

.. _python-isal: https://github.com/pycompression/python-isal

.. program:: gzip

.. _gzip-cli:

Command-line interface

The :mod:!gzip module provides a simple command line interface to compress or decompress files.

Once executed the :mod:!gzip module keeps the input file(s).

.. versionchanged:: 3.8

Add a new command line interface with a usage. By default, when you will execute the CLI, the default compression level is 6.

Command-line options ^^^^^^^^^^^^^^^^^^^^

.. option:: file

If file is not specified, read from :data:sys.stdin.

.. option:: --fast

Indicates the fastest compression method (less compression).

.. option:: --best

Indicates the slowest compression method (best compression).

.. option:: -d, --decompress

Decompress the given file.

.. option:: -h, --help

Show the help message.