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  • python标准库介绍——29 zlib 模块详解

    ==zlib 模块==
    
    
    (可选) ``zlib`` 模块为 "zlib" 压缩提供支持. (这种压缩方法是 "deflate".) 
    
    [Example 2-43 #eg-2-43] 展示了如何使用 ``compress`` 和 ``decompress`` 函数接受字符串参数.
    
    ====Example 2-43. 使用 zlib 模块压缩字符串====[eg-2-43]
    
    ```
    File: zlib-example-1.py
    
    import zlib
    
    MESSAGE = "life of brian"
    
    compressed_message = zlib.compress(MESSAGE)
    decompressed_message = zlib.decompress(compressed_message)
    
    print "original:", repr(MESSAGE)
    print "compressed message:", repr(compressed_message)
    print "decompressed message:", repr(decompressed_message)
    
    *B*original: 'life of brian'
    compressed message: 'x234313311LKU310OSH*312L3140300!1004302'
    decompressed message: 'life of brian'*b*
    ```
    
    文件的内容决定了压缩比率, [Example 2-44 #eg-2-44] 说明了这点.
    
    ====Example 2-44. 使用 zlib 模块压缩多个不同类型文件====[eg-2-44]
    
    ```
    File: zlib-example-2.py
    
    import zlib
    import glob
    
    for file in glob.glob("samples/*"):
    
        indata = open(file, "rb").read()
        outdata = zlib.compress(indata, zlib.Z_BEST_COMPRESSION)
    
        print file, len(indata), "=>", len(outdata),
        print "%d%%" % (len(outdata) * 100 / len(indata))
    
    *B*samplessample.au 1676 => 1109 66%
    samplessample.gz 42 => 51 121%
    samplessample.htm 186 => 135 72%
    samplessample.ini 246 => 190 77%
    samplessample.jpg 4762 => 4632 97%
    samplessample.msg 450 => 275 61%
    samplessample.sgm 430 => 321 74%
    samplessample.tar 10240 => 125 1%
    samplessample.tgz 155 => 159 102%
    samplessample.txt 302 => 220 72%
    samplessample.wav 13260 => 10992 82%*b*
    ```
    
    你也可以实时地压缩或解压缩数据, 如 [Example 2-45 #eg-2-45] 所示.
    
    ====Example 2-45. 使用 zlib 模块解压缩流====[eg-2-45]
    
    ```
    File: zlib-example-3.py
    
    import zlib
    
    encoder = zlib.compressobj()
    
    data = encoder.compress("life")
    data = data + encoder.compress(" of ")
    data = data + encoder.compress("brian")
    data = data + encoder.flush()
    
    print repr(data)
    print repr(zlib.decompress(data))
    
    *B*'x234313311LKU310OSH*312L3140300!1004302'
    'life of brian'*b*
    ```
    
    [Example 2-46 #eg-2-46] 把解码对象封装到了一个类似文件对象的类中, 
    实现了一些文件对象的方法, 这样使得读取压缩文件更方便.
    
    ====Example 2-46. 压缩流的仿文件访问方式====[eg-2-46]
    
    ```
    File: zlib-example-4.py
    
    import zlib
    import string, StringIO
    
    class ZipInputStream:
    
        def _ _init_ _(self, file):
            self.file = file
            self._ _rewind()
    
        def _ _rewind(self):
            self.zip = zlib.decompressobj()
            self.pos = 0 # position in zipped stream
            self.offset = 0 # position in unzipped stream
            self.data = ""
    
        def _ _fill(self, bytes):
            if self.zip:
                # read until we have enough bytes in the buffer
                while not bytes or len(self.data) < bytes:
                    self.file.seek(self.pos)
                    data = self.file.read(16384)
                    if not data:
                        self.data = self.data + self.zip.flush()
                        self.zip = None # no more data
                        break
                    self.pos = self.pos + len(data)
                    self.data = self.data + self.zip.decompress(data)
    
        def seek(self, offset, whence=0):
            if whence == 0:
                position = offset
            elif whence == 1:
                position = self.offset + offset
            else:
                raise IOError, "Illegal argument"
            if position < self.offset:
                raise IOError, "Cannot seek backwards"
    
            # skip forward, in 16k blocks
            while position > self.offset:
                if not self.read(min(position - self.offset, 16384)):
                    break
    
        def tell(self):
            return self.offset
    
        def read(self, bytes = 0):
            self._ _fill(bytes)
            if bytes:
                data = self.data[:bytes]
                self.data = self.data[bytes:]
            else:
                data = self.data
                self.data = ""
            self.offset = self.offset + len(data)
            return data
    
        def readline(self):
            # make sure we have an entire line
            while self.zip and "
    " not in self.data:
                self._ _fill(len(self.data) + 512)
            i = string.find(self.data, "
    ") + 1
            if i <= 0:
                return self.read()
            return self.read(i)
    
        def readlines(self):
            lines = []
            while 1:
                s = self.readline()
                if not s:
                    break
                lines.append(s)
            return lines
    
    #
    # try it out
    
    data = open("samples/sample.txt").read()
    data = zlib.compress(data)
    
    file = ZipInputStream(StringIO.StringIO(data))
    for line in file.readlines():
        print line[:-1]
    
    *B*We will perhaps eventually be writing only small
    modules which are identified by name as they are
    used to build larger ones, so that devices like
    indentation, rather than delimiters, might become
    feasible for expressing local structure in the
    source language.
        -- Donald E. Knuth, December 1974*b*
    ```
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  • 原文地址:https://www.cnblogs.com/xuchunlin/p/7763840.html
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