Python Namespaces and Scopes

First, the name space

definition : Name-to-object mapping. A namespace is an implementation of a dictionary, a key is a variable name, and a value is a value that corresponds to a variable. The namespaces are independent of each other and cannot have names in a namespace, but different namespaces can have duplicate names without any effect.

Classification:

1. Global namespace:

The namespace that is created when code is run.

2. Local namespaces:

A temporary space, such as a function, that is opened during a program's operation.

3. Built-in namespaces:

Open space for storing commonly used built-in methods, such as input,print,str,list, which are variables of the built-in namespaces before the program runs the load code

Plus loading sequence:   load Order: Built-in namespaces (pre-Program load)-Global namespaces (program run: Load from top to bottom) local namespaces (program run: Load only when called) Order of values: In the local call: Local namespace, global namespace, built-in namespaces, Global Call: Built-in namespaces, global namespaces

　　

Second, scope

Global scope: Contains built-in namespaces, global namespaces , can be referenced anywhere throughout the file, are globally valid

Local scope: Local namespace, only valid locally

Global keyword, nonlocal keyword.

Global

1, declare a global variable.

2, Global (limited to string, number) is required when local scope wants to make a modification to a globally scoped global variable.

Nonlocal:

1, global variables cannot be modified.

2, in the local scope, the variables of the parent scope (or the outer scope non-global scope) are referenced and modified, and which layer of the reference, from that layer and the following this variable all changed.

Python Namespaces and Scopes