Python -- filter，map

1.

filter:

Type:    builtin_function_or_method Base Class:  <type 'builtin_function_or_method'> String Form:  <built-in function filter> Namespace:  Python builtin Docstring:         filter(function or None, sequence) -> list, tuple, or string         Return those items of sequence for which function(item) is true.    If         function is None, return the items that are true.    If sequence is a tuple         or string, return the same type, else return a list.

2.

map:

Type:    builtin_function_or_method Base Class:  <type 'builtin_function_or_method'> String Form:  <built-in function map> Namespace:  Python builtin Docstring:         map(function, sequence[, sequence, ...]) -> list         Return a list of the results of applying the function to the items of         the argument sequence(s).    If more than one sequence is given, the         function is called with an argument list consisting of the corresponding         item of each sequence, substituting None for missing values when not all         sequences have the same length.    If the function is None, return a list of         the items of the sequence (or a list of tuples if more than one sequence).

3.

reduce:

Type:    builtin_function_or_method Base Class:  <type 'builtin_function_or_method'> String Form:  <built-in function reduce> Namespace:  Python builtin Docstring:         reduce(function, sequence[, initial]) -> value         Apply a function of two arguments cumulatively to the items of a sequence,         from left to right, so as to reduce the sequence to a single value.         For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates         ((((1+2)+3)+4)+5).    If initial is present, it is placed before the items         of the sequence in the calculation, and serves as a default when the         sequence is empty.

以上都是从ipython中截出来的官方Doc，放心理解。

等我深刻理解后会翻译出来的（没理解不敢翻译，怕误人子弟啦，呵呵）