Importing package in Python

Question

Scenario:

dirA/
   __init__.py
   file1.py
   file2.py
   dirB/
       __init__.py
       file11.py
       file22.py
       dirC/
           __init__.py
           file111.py
           file222.py

I read on https://docs.python.org/2/tutorial/modules.html#tut-standardmodules that Contrarily, when using syntax like import item.subitem.subsubitem, each item except for the last must be a package; the last item can be a module or a package but can’t be a class or function or variable defined in the previous item.

Now because of above reading i have a numbers on doubt:

1. When i do write import dirA.dirB so whether this statement import modules inside dirC package too or only the modules inside dirB ?

2. what is the use of import dirA.dirB, because when i am using this statement, am still unable to use the modules inside the dirB sub package ?

and i know that to use the modules inside dirB i have to use the import dirA.dirB.file11

Answer 1

When you do import dirA.dirB , you only import the package dirB , which means you basically import the __init__.py under dirB.py , if that __init__.py was defining some functions or classes etc, you would be able to use them after import dirA.dirB .

Example -

My directory structure -

shared/ a.py pkg/ init.py b.py

Now in pkg/__init__.py , I have -

x = 1
import pkg.b

My pkg/b.py is -

a = 1

Now in a.py , I can do -

import pkg
print(pkg.b.a)
print(pkg.x)

And this would work, because __init__.py imported pkg.b and hence it is accessible using pkg.b.a .

Answer 2

When you use from dirA import dirB, dirB will be a module which contains anything (variables, functions, etc) defined in or imported by dirB/__init__.py.

This is often used to make the "public" components of dirB easily accessible. For example, you might have:

from .file11 import Foo
from .file22 import Bar

So that users of your library could simply call:

from dirA.dirB import Foo, Bar

Instead of having to remember which file defines Foo and Bar.