| :mod:`gzip` --- Support for :program:`gzip` files |
| ================================================= |
| |
| .. module:: gzip |
| :synopsis: Interfaces for gzip compression and decompression using file objects. |
| |
| This module provides a simple interface to compress and decompress files just |
| like the GNU programs :program:`gzip` and :program:`gunzip` would. |
| |
| The data compression is provided by the :mod:`zlib` module. |
| |
| The :mod:`gzip` module provides the :class:`GzipFile` class. The :class:`GzipFile` |
| class reads and writes :program:`gzip`\ -format files, automatically compressing |
| or decompressing the data so that it looks like an ordinary :term:`file object`. |
| |
| Note that additional file formats which can be decompressed by the |
| :program:`gzip` and :program:`gunzip` programs, such as those produced by |
| :program:`compress` and :program:`pack`, are not supported by this module. |
| |
| For other archive formats, see the :mod:`bz2`, :mod:`zipfile`, and |
| :mod:`tarfile` modules. |
| |
| The module defines the following items: |
| |
| |
| .. class:: GzipFile(filename=None, mode=None, compresslevel=9, fileobj=None, mtime=None) |
| |
| Constructor for the :class:`GzipFile` class, which simulates most of the |
| methods of a :term:`file object`, with the exception of the :meth:`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 |
| :class:`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 :program:`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 :program:`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 :program:`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 :class:`GzipFile` object's :meth:`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 :class:`io.BytesIO` object opened for |
| writing as *fileobj*, and retrieve the resulting memory buffer using the |
| :class:`io.BytesIO` object's :meth:`~io.BytesIO.getvalue` method. |
| |
| :class:`GzipFile` supports the :class:`io.BufferedIOBase` interface, |
| including iteration and the :keyword:`with` statement. Only the |
| :meth:`truncate` method isn't implemented. |
| |
| .. versionchanged:: 3.1 |
| Support for the :keyword:`with` statement was added. |
| |
| .. versionchanged:: 3.2 |
| Support for zero-padded files was added. |
| |
| .. versionchanged:: 3.2 |
| Support for unseekable files was added. |
| |
| .. versionchanged:: 3.2 |
| The :meth:`peek` method was implemented. |
| |
| |
| .. function:: 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``. |
| |
| .. function:: compress(data, compresslevel=9) |
| |
| Compress the *data*, returning a :class:`bytes` object containing |
| the compressed data. *compresslevel* has the same meaning as in |
| the :class:`GzipFile` constructor above. |
| |
| .. versionadded:: 3.2 |
| |
| .. function:: decompress(data) |
| |
| Decompress the *data*, returning a :class:`bytes` object containing the |
| uncompressed data. |
| |
| .. versionadded:: 3.2 |
| |
| |
| .. _gzip-usage-examples: |
| |
| 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) |
| |
| .. seealso:: |
| |
| Module :mod:`zlib` |
| The basic data compression module needed to support the :program:`gzip` file |
| format. |
| |