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# 12.2. `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. 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.

For other archive formats, see the `bz2`, `zipfile`, and `tarfile` modules.

The module defines the following items:

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 `StringIO` 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 includes 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'`. If not given, the ‘b’ flag will be added to the mode to ensure the file is opened in binary mode for cross-platform portability.

  The compresslevel argument is an integer from `1` to `9` controlling the level of compression; `1` is fastest and produces the least compression, and `9` is slowest and produces the most 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` member 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.

    New in version 3.2.

  Changed in version 3.1: Support for the `with` statement was added.

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

  Changed in version 3.2: Support for unseekable files was added.

`gzip.``open`(filename, mode='rb', compresslevel=9)

  This is a shorthand for `GzipFile(filename,` `mode,` `compresslevel)`. The filename argument is required; mode defaults to `'rb'` and compresslevel defaults to `9`.

`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.

## 12.2.1. 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.

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