Python foundation - module (Standard Library)

1、 modular

1.1 What is a module

        python Standard libraries and built-in modules are not a concept , The standard library contains built-in modules , Built in modules belong to the standard library .

         For example, our common basic data types belong to python Standard library , But not built-in modules .

1.2 Module classification

• Built-in module
• Third-party module
• Custom module

2、 The import module

2.1 Import a single module

• import module         Import all members in the specified module （ Including variable 、 function 、 Class etc.
• import module as Alias     names
• from module import *     Only the members specified in the module will be imported

2.1 Import multiple modules

Method 1 ：import os,time,sys Each module is separated by English commas .

Method 2 ：import os

import time

import sys

Be careful ： It is recommended to use method 2 to import multiple modules , Import module sequence ： Built-in module ----> Third-party module ------> Custom module ;

The module is loaded into memory the first time it is imported , Follow up import Statement only adds a reference to a module object that has been loaded in large memory . Third party modules , A custom module may call a built-in module , therefore , When we import modules , You should first import the built-in module of the interpreter , Then import the third-party module , Finally, import the custom module .

3、 Import module failure reason and solution

3.1 Error message

Sometimes we will encounter import module failure , Error message ：ModuleNotFoundError: No module named ' Module name '.

3.2 Cause analysis

To solve this problem , We need to know Python The process of finding module files by the interpreter ：

• In the current directory , That is, find the directory where the currently executed program file is located ;
• To PYTHONPATH（ environment variable ） Find... In each of the directories below ;
• To Python Find in the default installation directory .

3.3 Solution

After knowing the reason , solve “Python Specified module not found ” The way to do this is 3 Kind of , Namely ：

• towards sys.path The full path of the storage location of the temporarily added module file in ;
• Place the module in sys.path The module already contained in the variable is in the loading path ;
• Set up path System environment variable .

reference:

What is a module ,Python Modular programming （ Entry required ）

Python Standard library — Python 3.8.12 file