问题
I want to know really what happens when we import a module file in python.I mean it's process, in other words what things by python will be run or check?! like __init__.py or sys.modules and etc.
for example i know __init__.py are necessary files in every package,i want to know python what does with these files on import time?
please light this for me.
回答1:
Read the tutorial section about modules, the documentation of the import statement, the imp module (particularly the examples) and maybe the docs for the __import__ builtin. That should get you a long way. If you still want to know more, I'd suggest to ask a specific question, this one is a bit on the broad side.
Edit: After reading your question once more, there is a specific part to your question, about what __init__.py does in packages. It basically can be empty or contain initialization code that will be executed when that package is imported. See the section about packages for details.
In an __init__.py you could also set __all__, which defines what symbols get imported when you do from yourpackage import *. This is explained in detail in importing * from a package.
来源：https://stackoverflow.com/questions/13128114/what-happens-when-import-modules-in-python