13.2. gzip — Support for gzip files

Source code: Lib/gzip.py

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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, as well as the open(), 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 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:

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 file object.

The filename argument can be an actual filename (a str or 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', or 'wb' for binary mode, or 'rt', 'at', or 'wt' for text mode. The default is 'rb'.

The compresslevel argument is an integer from 0 to 9, as for the GzipFile constructor.

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

For text mode, a GzipFile object is created, and wrapped in an io.TextIOWrapper instance with the specified encoding, error handling 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.

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 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 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', 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. To open a compressed file in text mode, use open() (or 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 truncate() method isn’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.

Note

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

New in version 3.2.

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

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.

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.

13.2.1. 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.