python import

Reference

world/
│
├── africa/
│   ├── __init__.py
│   └── zimbabwe.py
│
├── europe/
│   ├── __init__.py
│   ├── greece.py
│   ├── norway.py
│   └── spain.py
│
└── __init__.py

in this case, if every country file prints out a greeting, when __init__.py files selectively import some of the subpackages and submodules:

# world/africa/__init__.py  (Empty file)

# world/africa/zimbabwe.py
print("Shona: Mhoroyi vhanu vese")
print("Ndebele: Sabona mhlaba")

# world/europe/__init__.py
from . import greece
from . import norway

# world/europe/greece.py
print("Greek: Γειά σας Κόσμε")

# world/europe/norway.py
print("Norwegian: Hei verden")

# world/europe/spain.py
print("Castellano: Hola mundo")

# world/__init__.py
from . import africa

Note that world/__init__.py imports only africa and not europe. Similarly, world/africa/__init__.py doesn’t import anything, while world/europe/__init__.py imports greece and norway but not spain. Each country module will print a greeting when it’s imported.

>>> import world
>>> world
<module 'world' from 'world/__init__.py'>

>>> # The africa subpackage has been automatically imported
>>> world.africa
<module 'world.africa' from 'world/africa/__init__.py'>

>>> # The europe subpackage has not been imported
>>> world.europe
AttributeError: module 'world' has no attribute 'europe'

When europe is imported, the europe.greece and europe.norway modules are imported as well. You can see this because the country modules print a greeting when they’re imported:

>>> # Import europe explicitly
>>> from world import europe
Greek: Γειά σας Κόσμε
Norwegian: Hei verden

>>> # The greece submodule has been automatically imported
>>> europe.greece
<module 'world.europe.greece' from 'world/europe/greece.py'>

>>> # Because world is imported, europe is also found in the world namespace
>>> world.europe.norway
<module 'world.europe.norway' from 'world/europe/norway.py'>

>>> # The spain submodule has not been imported
>>> europe.spain
AttributeError: module 'world.europe' has no attribute 'spain'

>>> # Import spain explicitly inside the world namespace
>>> import world.europe.spain
Castellano: Hola mundo

>>> # Note that spain is also available directly inside the europe namespace
>>> europe.spain
<module 'world.europe.spain' from 'world/europe/spain.py'>

>>> # Importing norway doesn't do the import again (no output), but adds
>>> # norway to the global namespace
>>> from world.europe import norway
>>> norway
<module 'world.europe.norway' from 'world/europe/norway.py'>

The world/africa/__init__.py file is empty. This means that importing the world.africa package creates the namespace but has no other effect:

>>> # Even though africa has been imported, zimbabwe has not
>>> world.africa.zimbabwe
AttributeError: module 'world.africa' has no attribute 'zimbabwe'

>>> # Import zimbabwe explicitly into the global namespace
>>> from world.africa import zimbabwe
Shona: Mhoroyi vhanu vese
Ndebele: Sabona mhlaba

>>> # The zimbabwe submodule is now available
>>> zimbabwe
<module 'world.africa.zimbabwe' from 'world/africa/zimbabwe.py'>

>>> # Note that zimbabwe can also be reached through the africa subpackage
>>> world.africa.zimbabwe
<module 'world.africa.zimbabwe' from 'world/africa/zimbabwe.py'>

when executing python modules:

using python -m [submodules] to solve the import issues