Description of how map () and zip () operations are done in Python

for map () its prototype is: Map (function,sequence), which is to perform function functions on each element of the sequence sequence.

For example, the previous a,b,c = Map (Int,raw_input (). Split ()), meaning that the input a,b,c is converted to an integer. Another example:

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

The first map is to convert each element in list A to a list, and the second map converts each element in a to an integer.
For Zip (), the prototype is a ZIP (*list), List is a listing, and the 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 ]

To get the sum of each column, you need to unzip the list with a zip (*list) to get a list of tuples, where the I tuple contains the I element of each line:

[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 the zip and unzip (in fact, zip and * 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 (*zippe d) >>> X3 [1, 2, 3] >>> Y3 [4, 5, 6]