Introduction to map() and zip() operation methods in python

For map(), its prototype is: map(function, sequence), which is to perform function operations on each element in the sequence.

For example, the previous a, b, c = map(int, raw_input().split()) means to convert the input a, b, c into integers. Another example:

a = ['1','2','3','4']
print map(list,a)
print map(int,a)

The first map converts each element in list a into a list, and the second map converts each element in a is an integer.
For zip(), the prototype is zip(*list), list is a list, and zip(*list) returns a tuple, such as:

list = [[1,2,3],[4,5,6],[7,8,9]]
t = zip(*list)
print t

Output: [(1, 4, 7), (2, 5, 8), (3, 6, 9)]

x = [1,2,3,4,5]
y = [6,7,8,9,10]
a = zip(x,y)
print a

Output: [(1, 6), (2, 7), (3, 8), (4, 9), (5, 10)]

Here are some additions:

[python] 
>>> list = [[0,1,2],[3,1,4]] 
>>> [sum(x) for x in list] 
[3, 8] 
>>> map(sum,list) 
[3, 8]

If you want to get the sum of each column, you need to use zip(*list) to unzip the list first and get a tuple list, in which the i-th element The group contains the i-th element of each row:

[python] 
>>> list = [[0,1,2],[3,1,4]] 
>>> zip(*list) 
[(0, 3), (1, 1), (2, 4)] 
>>> [sum(x) for x in zip(*list)] 
[3, 2, 6] 
>>> map(sum,zip(*list)) 
[3, 2, 6]

The following example is about how zip and unzip (actually zip and * are used together) work ：

[python] 
>>> x=[1,2,3] 
>>> y=[4,5,6] 
>>> zipped = zip(x,y) 
>>> zipped 
[(1, 4), (2, 5), (3, 6)] 
>>> x2,y2=zip(*zipped) 
>>> x2 
(1, 2, 3) 
>>> y2 
(4, 5, 6) 
>>> x3,y3=map(list,zip(*zipped)) 
>>> x3 
[1, 2, 3] 
>>> y3 
[4, 5, 6]

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