python map/filter/reduce

python map/filter/reduce[转载]

原文:http://www.liuzhongshu.com/code/python-map-filter-reduce.html
python有几个内置的函数很有意思：map/filter/reduce，都是对一个集合进行处理，filter很容易理解用于过滤，map用于映射，reduce用于归并，这几个词还是太抽象了，下面的代码精确的说明了这几个函数的用途：

def map_imp(function, sequence) :

    if function is None: return list(sequence)

    retvals = []

    for element in sequence:

        if (function(element)):

            retvals.append(element)

            return retvals

def reduce_imp(function, sequence) :

    arg1 = function(sequence[0])

    for arg2 in sequence[1:] :

        arg1 = function(arg1, arg2)

    return arg1

def filter_imp(function, sequence) :

    retvals = []

    for element in sequence:

        if (function is None and element) or function(element) :

            retvals.append(element)

    return retvals

对于这种逻辑性强的东西，用语言来描述是无助的，代码则要清晰的多。

具体使用方法可以参考另外一篇:http://www.blogjava.net/rain1102/archive/2009/06/01/279478.html