Introduction to the usage and differences of nonlocal and global in Python3 (with examples)

This article brings you an introduction to the usage and difference between nonlocal and global in Python3 (with examples). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Keyword nonlocal

In Python 2.x, closures can only read the variables of the external function, but not overwrite it. In order to solve this problem, Python 3.x introduced the nonlocal keyword. Declaring variables with nonlocal within the closure allows the interpreter to find the variable name in the outer function.

Note: The keyword nonlocal: appears in python3.X, so it cannot be used directly in python2.x.
Keyword global

There are only two scopes in Python: Global scope and local scope. The global scope refers to the scope of the module where the current code is located, and the local scope refers to the scope of the current function or method. Code in the local scope can read variables in the external scope (including the global scope), but cannot change it. If you want to change it, you need to use the global keyword here

Example

The function of the keyword nonlocal is similar to the keyword global. The nonlocal keyword can be used to modify it in a nested function. Variables in nested scopes.
Look at two examples
Example 1

name = 'pythontab' def func() global name name = 'pythontab.com' func() print(name)

Result:

pythontab.com

Example 2

def func(): name = 'pythontab' def foo(): nonlocal name name = 'pythontab.com' foo() print(name) func()

Result:

pythontab.com

Note that in Example 2, the global keyword was not used to change the value of name.

Summary

The main differences are the following two points:

1. The functions of the two are different. After modifying a variable with the global keyword, it is marked as a global variable. Modifying the variable is to modify the global variable. After modifying the variable with the nonlocal keyword, it is marked as a local variable in the upper-level function. If there is no local variable in the upper-level function, If this local variable exists, an error will occur at the nonlocal location (the top-level function that uses nonlocal modified variables will definitely report an error).
2. The scope of use of the two is different. The global keyword can be used anywhere, including the top-level function and nested functions. Even if the variable has not been defined before, it can be used directly after global modification, while the nonlocal keyword can only be used in nested functions, and outside Corresponding local variables are defined in the layer function, otherwise an error will occur (see 1)

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