使用压缩并不总是会减少字符串的长度！
考虑下面的代码；
import zlibimport bz2def comptest(s): print 'original length:', len(s) print 'zlib compressed length:', len(zlib.compress(s)) print 'bz2 compressed length:', len(bz2.compress(s))
让我们在一个空字符串上尝试一下；
In [15]: comptest('')original length: 0zlib compressed length: 8bz2 compressed length: 14这样就
zlib产生了额外的8个字符和
bz214个字符。压缩方法通常在压缩数据前放置一个“标头”，以供解压缩程序使用。该头增加了输出的长度。
让我们测试一个单词；
In [16]: comptest('test')original length: 4zlib compressed length: 12bz2 compressed length: 40即使减去标题的长度，压缩也不会使单词变短。这是因为在这种情况下几乎没有压缩。字符串中的大多数字符仅出现一次。现在简短一句话；
In [17]: comptest('This is a compression test of a short sentence.')original length: 47zlib compressed length: 52bz2 compressed length: 73同样，压缩输出 大于 输入文本。由于文本的长度有限，因此重复很少，因此压缩效果不佳。
您需要相当长的文本块才能进行压缩，才能真正起作用。
In [22]: rings = ''' ....: Three Rings for the Elven-kings under the sky, ....: Seven for the Dwarf-lords in their halls of stone, ....: Nine for Mortal Men doomed to die, ....: One for the Dark Lord on his dark throne ....: In the Land of Mordor where the Shadows lie. ....: One Ring to rule them all, One Ring to find them, ....: One Ring to bring them all and in the darkness bind them ....: In the Land of Mordor where the Shadows lie.'''In [23]: comptest(rings) original length: 410zlib compressed length: 205bz2 compressed length: 248
