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 .

• Mahendra Gaur: what if nothing is written in pkg/__init__.py, what are the things will be loaded into memory when u will write import pkg inside a.py ?
• Anand S Kumar: nothing. only the module object for pkg , but you would not be able to do anything with it.
• Mahendra Gaur: ok, does it mean that importing the sub-package makes sense only if we have written code in the init.py ?
• Anand S Kumar: no, you can simply import the sub-package, like import pkg.b directly in a.py . But for pkg to be recognized as a package, you would need __init__.py in pkg folder.
• Mahendra Gaur: import pkg.b will load the module b, this is not the issue. i have issue with sub-package and what i mean is that definitely there will be a init.py file inside the package but if we have not written any thing in this file and import this package only such as import packagename then it will not make any sense, because we havn't written anything in init.py file

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.

• Mahendra Gaur: Thanku so much David Wolever.