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Summary of map() function in python

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1. About the map() function

(1) The map function is a built-in function in python for mapping.
(2) The map() function returns a new iterator object and will not change the original object!

2. Grammar

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.
 |  
 |  Methods defined here:
 |  
 |  __getattribute__(self, name, /)
 |      Return getattr(self, name).
 |  
 |  __iter__(self, /)
 |      Implement iter(self).
 |  
 |  __next__(self, /)
 |      Implement next(self).
 |  
 |  __reduce__(...)
 |      Return state information for pickling.
 |  
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |  
 |  __new__(*args, **kwargs) from builtins.type
 |      Create and return a new object.  See help(type) for accurate signature.

Simple understanding:

map(function, iterable)
#function -- 函数
#iterable -- 序列

In fact, the function of map() is very simple, you only need to remember one sentence: apply the function mapping to the sequence! !

3. Examples

(1) Use map() combined with split() for input
① Input str: a, b, c = input().split()
② Input integers: a, b, c = map(int, input().split( ))
③Input floating point numbers: a,b,c = map(float,input().split())

a,b,c = map(int,input().split(","))#此处function为int，序列即输入
print(a,b,c)
>>>1,2,3
>>>1 2 3

(2) map() returns an iterator

l = [2,0,0,2,0,2,2,2]
result = map(lambda x: x*x,l)
print(result)#返回一个迭代器
>>><map object at 0x000001DC51E22EC8>
print(list(result))#使用 list() 转换为列表
>>>[4, 0, 0, 4, 0, 4, 4, 4]
print(list(map(lambda x:x*x,l)))#合并为一行代码解决
>>>[4, 0, 0, 4, 0, 4, 4, 4]

Note: The map function will return an iterator, which is often converted using list().

Shallow records a small error (the code is as follows):

list = [2,0,0,2,0,2,2,2]
result = map(lambda x: x*x,list)
print(result)
print(list(result))

The result is an error:

TypeError: 'list' object is not callable

Demystification ( I never noticed this before! ):

I tried to convert the result returned by map() into a list list, but because the variable list and the function list have the same name , when the function uses the list function, it finds that list is a well-defined list, and the list cannot be called. Hence a TypeError is thrown.
(3) The function in the map is a custom function

def function(x):
    return x*2
print(list(map(function,range(3))))
>>>[0, 2, 4]

(4) The iterator is accessed only once

l = ['1', '2', '3', '4', '5', '6']
print(l)
>>>['1', '2', '3', '4', '5', '6']
l_int = map(lambda x: int(x), l)
for i in l_int:
    print(i, end=' ')
>>>1 2 3 4 5 6 
print()
print(list(l_int))
>>>[]#由于map()生成的是迭代器，所以for循环以后再使用l_int时迭代器中的数据已经为空了！！！