PaulZC / Absolute_Relativity

How to use absolute and relative imports in Python3

Absolute Relativity

It took me a long time to figure out where I was going wrong with relative and absolute imports in Python3. I'm sharing this to hopefully save you some time if you're attempting to do the same thing.

Thanks!

This post by BrenBarn really helped me figure out what was going on...

This post helped too:

Objective

To create nested packages with modules that can all be run individually as main.

.
└── Empty_init/
    ├── testMe.py
    └── Level_1/
        ├── __init__.py
        ├── I_Am_Level_1.py
        └── Level_2/
            ├── __init__.py
            ├── I_Am_Level_2.py
            └── Level_3/
                ├── __init__.py
                └── I_Am_Level_3.py

Simple right? Well, kind of. It took me a long time to figure out that you need to import the sub-packages differently depending on whether you are running as main or as an imported module. E.g.:

if __name__ == '__main__':
    from Level_3 import I_Am_Level_3
else:
    from .Level_3 import I_Am_Level_3

def Level_2():
    print("I am Level 2")
    I_Am_Level_3.Level_3()

if __name__ == '__main__':
    Level_2()

Empty __init__.py files

Level_3

cd Empty_init\Level_1\Level_2\Level_3
python I_Am_Level_3.py

produces:

• I am Level 3

Level_2

cd ..
python I_Am_Level_2.py

produces:

• I am Level 2
• I am Level 3

Level_1

cd ..
python I_Am_Level_1.py

produces:

• I am Level 1
• I am Level 2
• I am Level 3
• I am Level 3

Note that I am Level 3 appears twice - because it is printed by both Level_2() and Level_3()

main

cd ..
python testMe.py

produces:

• I Am Main
• I am Level 1
• I am Level 2
• I am Level 3
• I am Level 3
• I am Level 2
• I am Level 3
• I am Level 3

testMe.py is:

from Level_1 import I_Am_Level_1
from Level_1.Level_2 import I_Am_Level_2
from Level_1.Level_2.Level_3 import I_Am_Level_3

def runTest():
    print("I Am Main")
    I_Am_Level_1.Level_1()
    I_Am_Level_2.Level_2()
    I_Am_Level_3.Level_3()

runTest()

Populated __init__.py files

For more absolute relative fun, check out the With_init folder:

.
└── With_init/
    ├── testMe.py
    └── Level_1/
        ├── __init__.py
        ├── I_Am_Level_1.py
        └── Level_2/
            ├── __init__.py
            ├── I_Am_Level_2.py
            └── Level_3/
                ├── __init__.py
                └── I_Am_Level_3.py

E.g. __init__.py in Level_2 can be:

from .I_Am_Level_2 import Level_2

testMe.py can be simplified to:

import Level_1

def runTest():
    print("I Am Main")
    Level_1.I_Am_Level_1.Level_1()
    Level_1.Level_2.I_Am_Level_2.Level_2()
    Level_1.Level_2.Level_3.I_Am_Level_3.Level_3()

runTest()

No I_Am_

Do we need those helpful I_Am_'s in the module names? No, not really. Try the No_I_Am folder for more absolute relative headache-inducing fun!

.
└── No_I_Am/
    ├── testMe.py
    └── Level_1/
        ├── __init__.py
        ├── Level_1.py
        └── Level_2/
            ├── __init__.py
            ├── Level_2.py
            └── Level_3/
                ├── __init__.py
                └── Level_3.py

testMe.py can be simplified to:

import Level_1

def runTest():
    print("I Am Main")
    Level_1.Level_1()
    Level_1.Level_2.Level_2()
    Level_1.Level_2.Level_3.Level_3()

runTest()

Enjoy!

Paul