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pythonmkv

result when __all__ is not defined in __init__.py of package?

I am just learning and practicing python,on the way,i am reading about python packages and how to import into other modules or package at Modules ,I assume the following scenario ,

I have package as ,

Video/
    __init__.py
    formats/
        __init__.py 
        mkv.py  
        mp4.py
    length/
        __init__.py
        morethan20min.py
        lessthan20min.py

and in no 

__init__.py

I have not defined

__all__

what happens if i have an import statement as,

import Video.format.mkv
import Video.formats.*

Since I have already imported mkv module in first statement,what exactly happens after execution of second import statement,I didnt get the concept after reading on the mentioned link.

Solution

  • When you do

    from whatever_package import *

    first, if the package's __init__.py hasn't been run yet, it will be run. (If you've already done import whatever_package.something_specific, the package's __init__.py will have already been run.)

    Then, if whatever_package.__init__ does not define an __all__ list, the import will pick up all current contents of the whatever_package object*. That'll be anything defined in __init__.py and any submodules that have already been explicitly imported by any code that has executed in your program. For example, if whatever_package's __init__.py is empty, you do

    import whatever_package.something_specific
from whatever_package import *
import whatever_package.other_thing

    and no other import statements relating to whatever_package exist in your program, then the import * will pick up something_specific, but not any other submodules of whatever_package, such as other_thing.

    *excluding anything that begins with an underscore, as is standard for any import * with no __all__ list, whether you're importing from a package or a normal module.