gzip — Support for gzip files (2024)

Source code: Lib/gzip.py

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

The data compression is provided by the zlib module.

The gzip module provides the GzipFile class, as well as theopen(), compress() and decompress() convenience functions.The GzipFile class reads and writes gzip-format files,automatically compressing or decompressing the data so that it looks like anordinary file object.

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

The module defines the following items:

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

Open a gzip-compressed file in binary or text mode, returning a fileobject.

The filename argument can be an actual filename (a str orbytes 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 theGzipFile constructor.

For binary mode, this function is equivalent to the GzipFileconstructor: GzipFile(filename, mode, compresslevel). In this case, theencoding, errors and newline arguments must not be provided.

For text mode, a GzipFile object is created, and wrapped in anio.TextIOWrapper instance with the specified encoding, errorhandling behavior, and line ending(s).

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

Changed in version 3.4: Added support for the 'x', 'xb' and 'xt' modes.

Changed in version 3.6: Accepts a path-like object.

exception gzip.BadGzipFile

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

Added in version 3.8.

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

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

The new class instance is based on fileobj, which can be a regular file, anio.BytesIO object, or any other object which simulates a file. Itdefaults to None, in which case filename is opened to provide a fileobject.

When fileobj is not None, the filename argument is only used to beincluded in the gzip file header, which may include the originalfilename of the uncompressed file. It defaults to the filename of fileobj, ifdiscernible; otherwise, it defaults to the empty string, and in this case theoriginal 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 orwritten. The default is the mode of fileobj if discernible; otherwise, thedefault is 'rb'. In future Python releases the mode of fileobj willnot 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 filein text mode, use open() (or wrap your GzipFile with anio.TextIOWrapper).

The compresslevel argument is an integer from 0 to 9 controllingthe level of compression; 1 is fastest and produces the leastcompression, and 9 is slowest and produces the most compression. 0is no compression. The default is 9.

The mtime argument is an optional numeric timestamp to be written tothe last modification time field in the stream when compressing. Itshould only be provided in compression mode. If omitted or None, thecurrent time is used. See the mtime attribute for more details.

Calling a GzipFile object’s close() method does not closefileobj, since you might wish to append more material after the compresseddata. This also allows you to pass an io.BytesIO object opened forwriting as fileobj, and retrieve the resulting memory buffer using theio.BytesIO object’s getvalue() method.

GzipFile supports the io.BufferedIOBase interface,including iteration and the with statement. Only thetruncate() method isn’t implemented.

GzipFile also provides the following method and attribute:


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


While calling peek() does not change the file position ofthe GzipFile, it may change the position of the underlyingfile object (e.g. if the GzipFile was constructed with thefileobj parameter).

Added in version 3.2.


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

All gzip compressed streams are required to contain thistimestamp field. Some programs, such as gunzip, make useof the timestamp. The format is the same as the return value oftime.time() and the st_mtime attribute ofthe object returned by os.stat().


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

Changed in version 3.1: Support for the with statement was added, along with themtime constructor argument and mtime attribute.

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

Changed in version 3.3: The io.BufferedIOBase.read1() method is now implemented.

Changed in version 3.4: Added support for the 'x' and 'xb' modes.

Changed in version 3.5: Added support for writing arbitrarybytes-like objects.The read() method now accepts an argument ofNone.

Changed in version 3.6: Accepts a path-like object.

Changed in version 3.12: Remove the filename attribute, use the nameattribute instead.

Deprecated since version 3.9: Opening GzipFile for writing without specifying the modeargument is deprecated.

gzip.compress(data, compresslevel=9, *, mtime=None)

Compress the data, returning a bytes object containingthe compressed data. compresslevel and mtime have the same meaning as inthe GzipFile constructor above. When mtime is set to 0, thisfunction is equivalent to zlib.compress() with wbits set to 31.The zlib function is faster.

Added in version 3.2.

Changed in version 3.8: Added the mtime parameter for reproducible output.

Changed in version 3.11: Speed is improved by compressing all data at once instead of in astreamed fashion. Calls with mtime set to 0 are delegated tozlib.compress() for better speed.


Decompress the data, returning a bytes object containing theuncompressed data. This function is capable of decompressing multi-membergzip data (multiple gzip blocks concatenated together). When the data iscertain to contain only one member the zlib.decompress() function withwbits set to 31 is faster.

Added in version 3.2.

Changed in version 3.11: Speed is improved by decompressing members at once in memory instead of ina streamed fashion.

Examples of usage

Example of how to read a compressed file:

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

Example of how to create a compressed GZIP file:

import gzipcontent = 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 gzipimport shutilwith 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 gzips_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 fileformat.

Command Line Interface

The gzip module provides a simple command line interface to compress ordecompress files.

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

Changed in version 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


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


Indicates the fastest compression method (less compression).


Indicates the slowest compression method (best compression).

-d, --decompress

Decompress the given file.

-h, --help

Show the help message.

gzip — Support for gzip files (2024)
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