Python's expanded knowledge of + = and =

Source: Internet
Author: User

There are two points on the internet, and I want to say something.


Online has always said num = num + num and num + = num is equivalent, here I want to say, these two only when NUM is a numeric value is equivalent, if not numeric,num = num + num is the value of NUM Plus num is assigned to NUM, which One is to create a new space for Num, and num+=num is the result of modifying Num's original value to num + num . Maybe you'll be a little stunned, okay, let's look at the example below

A = [100]def Zhouyu (num): num = num + num print (num) Zhouyu (a) print (a)

With the above understanding, we know that num = num + num is actually assigning the result of [100] plus [100] to NUM, and then Num will go back to that result and say that if the value of NUM is [100], then the value of NUM is now [100,100] , while A is still [100].

Here's another one.

A = [100]def Zhouyu (num): num + = num print (num) Zhouyu (a) print (a)

Because Num +=num actually modifies the value of NUM itself, it modifies the value of NUM and the value of a is changed.


Compare the results of the following two paragraphs of code

A = 100def Zhouyu (num): num +=num print (num) Zhouyu (a) print (a)

Why is the result of execution



Because A is an integer type, except the list and the dictionary is basically immutable, Zhouyu (a) is passed a, so Num will point to a, because a=100 is an integer type, is immutable, so here will go to create a new a,a=100+100, so A is 200, Print out is 200, and the outside of a is that a so, it is still 100. If you don't understand it, see below.

A = [100]def Zhouyu (num): num +=num print (num) Zhouyu (a) print (a)

Why is the result of execution the following result?



Because Zhouyu (a) is passing in a, num points to a, where a is a list type and can be changed. So it will change the above, and the print will change. That is, when the parameter is passed to see if a is mutable, if it is mutable will change the value of the outside, if not mutable, it is a new creation of a, this time the value of a and function outside the value is not the same

This article is from "Love Zhou Yu" blog, please be sure to keep this source

Python's expanded knowledge of + = and =

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