# `gzip` --- 对 gzip 格式的支持

源代码： Lib/gzip.py

此模块提供的简单接口帮助用户压缩和解压缩文件，功能类似于 GNU 应用程序 gzip 和 gunzip。

数据压缩由 `zlib` 模块提供。

`gzip` 模块提供 `GzipFile` 类和便利的 `open()`、`compress()`、`decompress()` 函数。`GzipFile` 类读写 gzip 格式的文件，同时自动压缩和解压缩数据，这让操作压缩文件如同操作普通的 file object 一样方便。

注意，此模块不支持部分可以被 gzip 和 gunzip 解压的格式，如利用 compress 或 pack 压缩所得的文件。

这个模块定义了以下内容：

`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).

  在 3.3 版更改: Added support for filename being a file object, support for text mode, and the encoding, errors and newline arguments.

  在 3.4 版更改: Added support for the `'x'`, `'xb'` and `'xt'` modes.

  在 3.6 版更改: 接受一个 类路径对象。

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'`.

  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.

    注解

    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).

    3.2 新版功能.

  `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()`.

  在 3.1 版更改: Support for the `with` statement was added, along with the mtime constructor argument and `mtime` attribute.

  在 3.2 版更改: Support for zero-padded and unseekable files was added.

  在 3.3 版更改: The `io.BufferedIOBase.read1()` method is now implemented.

  在 3.4 版更改: Added support for the `'x'` and `'xb'` modes.

  在 3.5 版更改: Added support for writing arbitrary bytes-like objects. The `read()` method now accepts an argument of `None`.

  在 3.6 版更改: 接受一个 类路径对象。

`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.

  3.2 新版功能.

  在 3.8 版更改: Added the mtime parameter for reproducible output.

`gzip.``decompress`(data)

  Decompress the data, returning a `bytes` object containing the uncompressed data.

  3.2 新版功能.

## 用法示例

如何读取一个压缩文件：

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

如何创建一个 GZIP 文件：

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

如何使用 GZIP 压缩一个已有的文件：

    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)

如何使用 GZIP 压缩一个二进制串：

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

参见

模块 `zlib`
  支持 gzip 格式所需要的基本压缩模块。

## 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).

在 3.8 版更改: 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.