gzip — Support for gzip files

Source code: Lib/gzip.py

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', '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 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).

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

Cambiato nella versione 3.4: Added support for the 'x', 'xb' and 'xt' modes.

Cambiato nella versione 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 gzip files.

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 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, an 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', '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 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 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 mtime attribute that is set when decompressing.

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 an 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 and attribute:

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.

Nota

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).

Added in version 3.2.

mode

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

Cambiato nella versione 3.13: In previous versions it was an integer 1 or 2.

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.

name

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.

Cambiato nella versione 3.1: Support for the with statement was added, along with the mtime constructor argument and mtime attribute.

Cambiato nella versione 3.2: Support for zero-padded and unseekable files was added.

Cambiato nella versione 3.3: The io.BufferedIOBase.read1() method is now implemented.

Cambiato nella versione 3.4: Added support for the 'x' and 'xb' modes.

Cambiato nella versione 3.5: Added support for writing arbitrary bytes-like objects. The read() method now accepts an argument of None.

Cambiato nella versione 3.6: Accepts a path-like object.

Deprecato dalla versione 3.9: Opening GzipFile for writing without specifying the mode argument is deprecated.

Cambiato nella versione 3.12: Remove the filename attribute, use the name attribute instead.

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

Compress the data, returning a bytes object containing the compressed data. compresslevel and mtime have the same meaning as in the GzipFile constructor above.

Added in version 3.2.

Cambiato nella versione 3.8: Added the mtime parameter for reproducible output.

Cambiato nella versione 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 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.

Cambiato nella versione 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.

gzip.decompress(data)

Decompress the data, returning a 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 zlib.decompress() function with wbits set to 31 is faster.

Added in version 3.2.

Cambiato nella versione 3.11: Speed is improved by decompressing members at once in memory instead of in a streamed fashion.

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)

Vedi anche

Module zlib

The basic data compression module needed to support the gzip file format.

Command Line Interface

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

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

Cambiato nella versione 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

file

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

--fast

Indicates the fastest compression method (less compression).

--best

Indicates the slowest compression method (best compression).

-d, --decompress

Decompress the given file.

-h, --help

Show the help message.