python的模块和包机制：import和from..import.._from import可以引入包-优快云博客

本文链接：https://blog.youkuaiyun.com/vincent2610/article/details/53787350

本文探讨了Python中的模块和包机制，重点解析import和from...import...的使用方式，通过官方文档和Stack Overflow的回答，帮助读者深化对这两个导入语句的理解。

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写python一段时间了，但是对import和from import却没有深刻的认识。借由官方文档https://docs.python.org/2/tutorial/modules.html，和stackoverflow上的回答对这两个导入语句有了一些了解。

一. 两个概念：

1.module

A module is a file containing Python definitions and statements.

所以module就是一个.py文件

2.package

Packages are a way of structuring Python’s module namespace by using “dotted module names”
……
The __init__.py files are required to make Python treat the directories as containing packages; 
……

所以package就是一个包含.py文件的文件夹，文件夹中还包含一个特殊文件__.init__.py

二. import和from import的用法

import package1  #✅
import module  #✅
from module import function  #✅
from package1 import module  #✅
from package1.package2 import  #✅
import module.function1  #❌

三. import和from import的含义

来自stackoverflow

import X :

imports the module X, and creates a reference to that module in the current
namespace. Then you need to define completed module path to access a
particular attribute or method from inside the module.

from X import * :

*imports the module X, and creates references to all public objects
   defined by that module in the current namespace (that is, everything
   that doesn’t have a name starting with “_”) or what ever the name
   you mentioned.
   Or in other words, after you’ve run this statement, you can simply
   use a plain name to refer to things defined in module X. But X itself
   is not defined, so X.name doesn’t work. And if name was already
   defined, it is replaced by the new version. And if name in X is
   changed to point to some other object, your module won’t notice.

* This makes all names from the module available in the local namespace.