以下是filter函數(shù)的官方文檔，注意最后一段，當(dāng)function不為None時，函數(shù)相似于[item for item in iterable if function(item)]，function為None時，函數(shù)相似于[item for item in iterable if item]。

filter(function, iterable)
Construct a list from those elements of iterable for which function returns true. iterable may be either a sequence, a container which supports iteration, or an iterator. If iterable is a string or a tuple, the result also has that type; otherwise it is always a list. If function is None, the identity function is assumed, that is, all elements of iterable that are false are removed.
Note that filter(function, iterable) is equivalent to [item for item in iterable if function(item)] if function is not None and [item for item in iterable if item] if function is None.

根據(jù)官方文檔，為了方便理解，自己試著去實(shí)現(xiàn)了下，沒有帶異常處理。分析filter(function, iterable)，滿足以下條件

• function, 為None, 或者函數(shù)。
  
• iterable, 為list, tuple, 或者basestring。

根據(jù)function生成列表，再根據(jù)iterable對列表進(jìn)行相應(yīng)處理。

def myFilter(func, seq):    if func is None:        results = [i for i in seq if i]    else:        results = [i for i in seq if func(i)]    if isinstance(seq, tuple):        results = tuple(results)    elif isinstance(seq, basestring):        results = ''.join(results)    return results

運(yùn)行結(jié)果與filter自建函數(shù)輸出一致。

PRint '-------------------filter------------------------------'print filter(lambda x: x > 4, range(10))print filter(lambda x: x > 4, tuple(range(10)))print filter(None, range(10))print filter(lambda x: x > '3', '12345')print filter(None, '01234')print '-------------------myFilter----------------------------'print myFilter(lambda x: x > 4, range(10))print myFilter(lambda x: x > 4, tuple(range(10)))print myFilter(None, range(10))print myFilter(lambda x: x > '3', '12345')print myFilter(None, '01234')