# `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).

  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 `OSError`. `EOFError` and `zlib.error` can also be raised for invalid gzip files.

  New 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 mtime argument is an optional numeric timestamp to be written to the last modification time field in the stream when compressing. It should only be provided in compression mode. If omitted or `None`, the current time is used. See the `mtime` attribute for more details.

  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.

    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.

  mtime

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

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

  Changed in version 3.1: Support for the `with` statement was added, along with the mtime 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 arbitrary bytes-like objects. The `read()` method now accepts an argument of `None`.

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

  Deprecated since version 3.9: Opening `GzipFile` for writing without specifying the mode argument is deprecated.

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. When mtime is set to `0`, this function is equivalent to `zlib.compress()` with wbits set to `31`. The zlib function is faster.

  New 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 a streamed fashion. Calls with mtime set to `0` are delegated to `zlib.compress()` for better speed.

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.

  New in version 3.2.

  Changed in version 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)

See also

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).

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

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.