"gzip" --- **gzip** 檔案的支援
******************************

**原始碼：**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 可選
模組的需求.

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.

此模組定義了以下項目：

gzip.open(filename, mode='rb', compresslevel=6, 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).

   在 3.3 版的變更: Added support for *filename* being a file object,
   support for text mode, and the *encoding*, *errors* and *newline*
   arguments.

   在 3.4 版的變更: 新增 "'x'"、"'xb'" 和 "'xt'" 模式的支援。

   在 3.6 版的變更: 接受*類路徑物件*。

   在 3.15 版的變更: The default compression level was reduced to 6
   (down from 9). It is the default level used by most compression
   tools and a better tradeoff between speed and performance.

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.

   在 3.8 版被加入.

class gzip.GzipFile(filename=None, mode=None, compresslevel=6, 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" 也提供了以下的方法和屬性：

   peek(n)

      Read *n* uncompressed bytes without advancing the file position.
      The number of bytes returned may be more or less than requested.

      備註:

        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).

      在 3.2 版被加入.

   mode

      "'rb'" 用於讀取、"'wb'" 用於寫入。

      在 3.13 版的變更: 在先前版本中它是整數 "1" 或 "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.

   在 3.1 版的變更: Support for the "with" statement was added, along
   with the *mtime* constructor argument and "mtime" attribute.

   在 3.2 版的變更: Support for zero-padded and unseekable files was
   added.

   在 3.3 版的變更: "io.BufferedIOBase.read1()" 方法現在已有實作。

   在 3.4 版的變更: 新增 "'x'" 和 "'xb'" 模式的支援。

   在 3.5 版的變更: Added support for writing arbitrary *bytes-like
   objects*. The "read()" method now accepts an argument of "None".

   在 3.6 版的變更: 接受*類路徑物件*。

   在 3.9 版之後被棄用: Opening "GzipFile" for writing without
   specifying the *mode* argument is deprecated.

   在 3.12 版的變更: Remove the "filename" attribute, use the "name"
   attribute instead.

   在 3.15 版的變更: The default compression level was reduced to 6
   (down from 9). It is the default level used by most compression
   tools and a better tradeoff between speed and performance.

gzip.compress(data, compresslevel=6, *, 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.

   在 3.2 版被加入.

   在 3.8 版的變更: Added the *mtime* parameter for reproducible
   output.

   在 3.11 版的變更: 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.

   在 3.13 版的變更: 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.

   在 3.14 版的變更: The *mtime* parameter now defaults to 0 for
   reproducible output. For the previous behaviour of using the
   current time, pass "None" to *mtime*.

   在 3.15 版的變更: The default compression level was reduced to 6
   (down from 9). It is the default level used by most compression
   tools and a better tradeoff between speed and performance.

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.

   在 3.2 版被加入.

   在 3.11 版的變更: Speed is improved by decompressing members at
   once in memory instead of in a streamed fashion.


用法範例
========

如何讀取壓縮檔案的範例：

   import gzip
   with gzip.open('/home/joe/file.txt.gz', 'rb') as f:
       file_content = f.read()

如何建立一個壓縮的 GZIP 檔案的範例：

   import gzip
   content = b"Lots of content here"
   with gzip.open('/home/joe/file.txt.gz', 'wb') as f:
       f.write(content)

如何壓縮一個已存在的檔案的範例：

   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)

如何壓縮一個二進位字串的範例：

   import gzip
   s_in = b"Lots of content here"
   s_out = gzip.compress(s_in)

也參考:

  "zlib" 模組
     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.


命令列介面
==========

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

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

在 3.8 版的變更: Add a new command line interface with a usage. By
default, when you will execute the CLI, the default compression level
is 6.


命令列選項
----------

file

   如果未指定 *file*，則從 "sys.stdin" 讀取。

--fast

   Indicates the fastest compression method (less compression).

--best

   Indicates the slowest compression method (best compression).

-d, --decompress

   解壓縮指定的檔案。

-h, --help

   顯示幫助訊息。
