g – 5 – filter

filter(function or None, iterable):
        1 过滤掉不符合条件的元素
        2 函数为真返回，为假不返回
        3 class filter(function or None, iterable):
        4 filter(function or None, iterable) --> filter object
        5 $Exp:
            $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
            $  print(
            $      list(filter(None,[1,2,3])),             #[1, 2, 3]
            $      list(filter(lambda x : x>=3,[1,2,3])),  #[3]
            $  )
            $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$