Import paths - the right way?

What is the entry point for your program? Usually the entry point for a program will be at the root of the project. Since it is at the root, all the modules within the root will be importable, provided there is an __init__.py file in them.

So, using your example:

my_project/
    main.py
    package1/
        __init__.py
        module1
        module2
    package2/
        __init__.py
        module1
        module2

main.py would be the entry point for your program. Because the file that is executed as main is automatically put on the PYTHONPATH, both package1 and package2 are available from the top level import.

# in main.py
from package1.module1 import *
from package1.module2 import *

# in package1.module1
import module2
from package2.module1 import *

# in package2.module1 import *
import module2
from package1.module1 import *

Note that in the above, package1 and package2 depend on each other. That should never be the case. But this is just an example of being able to import from anywhere.

main.py doesn't have to be anything fancy either. It can be very simple:

# main.py

if __name__ == '__main__':
    from package1.module1 import SomeClass
    SomeClass().start()

The point I'm trying to make, is that if a module needs to be accessible by other modules, that module should be available as a top level import. A module should not attempt to put itself as a top level import (directly on the PYTHONPATH).

It should be the responsibility of the project for ensuring that all imports can be satisfied if the module is included directly in the project. There are two ways to do this. The first is by creating a bootstrapper file such as main.py in the project folder. The other, is by creating a file that adds all relevant paths to PYTHONPATH, that is loaded by any entry points that may exist.

For example:

# setup.py
import sys

def load():
    paths = ['/path1/','/path2/','/path3/']
    for p in path:
        sys.path.insert(0, p)

# entrypoint.py
from setup import load
load()
# continue with program

The main thing to take away, is that a module is not supposed to put itself on the path. The path should be determined automatically by the entry point into the program, or defined explicitly by a setup script that knows where all the relevant modules are.

I generally create each package as an installable package (ie, create a setup.py file), and then install them into a virtualenv just for this project, using pip.

You can even install the using pip -e if they are still under development.

Import paths - the right way?

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