内置函数--map，filter，reduce

Posted 2020-09-30 阿木

一、map

class map(object):
    """
    map(func, *iterables) --> map object
    
    Make an iterator that computes the function using arguments from
    each of the iterables.  Stops when the shortest iterable is exhausted.
    """
    def __getattribute__(self, *args, **kwargs): # real signature unknown
        """ Return getattr(self, name). """
        pass

    def __init__(self, func, *iterables): # real signature unknown; restored from __doc__
        pass

    def __iter__(self, *args, **kwargs): # real signature unknown
        """ Implement iter(self). """
        pass

    @staticmethod # known case of __new__
    def __new__(*args, **kwargs): # real signature unknown
        """ Create and return a new object.  See help(type) for accurate signature. """
        pass

    def __next__(self, *args, **kwargs): # real signature unknown
        """ Implement next(self). """
        pass

    def __reduce__(self, *args, **kwargs): # real signature unknown
        """ Return state information for pickling. """
        pass

View Code

map(func, *iterables) --> map object
　　Make an iterator that computes the function using arguments from
　　each of the iterables.  Stops when the shortest iterable is exhausted.
　　"""

　　使用从参数来计算函数的迭代器每个迭代项。在最短的迭代结束时停止。

 

遍历序列，对序列中每个元素进行操作，最终获取新的序列。

给li = [1,2,3,4]每个元素加100

#!/usr/bin/python3

li = [1,2,3,4]

newList = map(lambda x:x+100, li)
print(newList)
print(list(newList))

执行结果：

<map object at 0x00000000027C4C88>
[101, 102, 103, 104]

参数传入自定义函数：

#!/usr/bin/python3

li = [1,2,3,4]

def myAdd (x):
    return x * 100

newList = map(myAdd, li)
print(newList)
print(list(newList))

执行结果：

<map object at 0x00000000022249B0>
[100, 200, 300, 400]

二、filter

class filter(object):
    """
    filter(function or None, iterable) --> filter object
    
    Return an iterator yielding those items of iterable for which function(item)
    is true. If function is None, return the items that are true.
    """
    def __getattribute__(self, *args, **kwargs): # real signature unknown
        """ Return getattr(self, name). """
        pass

    def __init__(self, function_or_None, iterable): # real signature unknown; restored from __doc__
        pass

    def __iter__(self, *args, **kwargs): # real signature unknown
        """ Implement iter(self). """
        pass

    @staticmethod # known case of __new__
    def __new__(*args, **kwargs): # real signature unknown
        """ Create and return a new object.  See help(type) for accurate signature. """
        pass

    def __next__(self, *args, **kwargs): # real signature unknown
        """ Implement next(self). """
        pass

    def __reduce__(self, *args, **kwargs): # real signature unknown
        """ Return state information for pickling. """
        pass

View Code

filter(function or None, iterable) --> filter object

　　Return an iterator yielding those items of iterable for which function(item)
　　is true. If function is None, return the items that are true.
　　"""
　　返回一个迭代器，该迭代器可以为该函数(项)进行迭代是真的。如果函数是None，返回true的项。

 

对于序列中的元素进行筛选，最终获取符合条件的序列

#filter第一个参数为空，将获取原来序列

 

#!/usr/bin/python3

li = [1,2,3,4,5,6,7,8,9,10]

def myAdd (x):
    return x % 2 == 0

newList = filter(myAdd, li)
print(newList)
print(list(newList))

print("---------------")
newList = filter(lambda x: x % 2 , li)
print(newList)
print(list(newList))

print("---------------")
#filter第一个参数为空，将获取原来序列
newList = filter(None, li)
print(newList)
print(list(newList))

执行结果：

<filter object at 0x0000000002824EB8>
[2, 4, 6, 8, 10]
---------------
<filter object at 0x000000000282B320>
[1, 3, 5, 7, 9]
---------------
<filter object at 0x0000000002824EB8>
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]