"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.

This is an *optional module*. If it is missing from your copy of
CPython, look for documentation from your distributor (that is,
whoever provided Python to you). If you are the distributor, see
Requirements for optional modules.

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.
      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=0)

   Compress the *data*, returning a "bytes" object containing the
   compressed data.  *compresslevel* and *mtime* have the same meaning
   as in the "GzipFile" constructor above, but *mtime* defaults to 0
   for reproducible output.

   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.

   Cambiato nella versione 3.14: The *mtime* parameter now defaults to
   0 for reproducible output. For the previous behaviour of using the
   current time, pass "None" to *mtime*.

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.

  In case gzip (de)compression is a bottleneck, the python-isal
  package speeds up (de)compression with a mostly compatible API.


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.
