How to correctly make a python package?

Question

This is my first time making a python package, and I am thoroughly confused about __init__.py, __main__.py, and their relation to making a package.

Here is my project structure:

package_name/
    setup.py
    README.md
    LICENSE
    package_name/
        __init__.py
        __main__.py
        A.py
        B.py

Class A in A.py depends on a class B in B.py.

Should I have both __init__.py and __main__.py? What should be in the files?

What I have tried:

in A.py:

from B import B and from .B import B

The first allows me to run normally locally, but when I try to upload it to pypi and install it, I get ModuleNotFoundError: No module named 'B'

The second allows me to import it after installing it from pypi, but I can't run it normal locally.

My goal is to import Class A from the package with the following

from package_name import A

and be able to run my package locally.

Edit: I am using Python 3.

Are you using python 3 or 2? Usually you don't need to include `__main__.py` in either, that's for more specific needs. — Zhenhir, Jun 28 '19 at 05:16
`ModuleNotFoundError: No module named 'B'` means that your `B.py` is not found in `syspath`. You can try to manually add it during runtime in `__init__.py`. — Raguel, Jun 28 '19 at 05:30

score 1 · Accepted Answer · edited May 25 '23 at 15:01

Files named init.py are used to mark directories on disk as a Python package directories, you can let this empty most of the time.

But let's say you have for example this file structure with the following code inside them:

Structure

    package_name/
    ├── setup.py
    ├── package_name
    │   ├── __init__.py
    │   └── main.py
    └── package_name.py

setup.py

#!/usr/bin/env python3
import sys
from setuptools import setup

setup(
    name = "package_name",        
    version = "0.1",
    packages=["package_name"],   
    package_data = {},
    author="xxx",
    author_email = "xxx@xxx.xx",
    description = "The familiar example program in Python",
    license = "BSD",
    keywords= "example documentation tutorial",
)

package_name.py

#!/usr/bin/env python
import sys
import package_name.main

if __name__ == '__main__':
    sys.exit(package_name.main.main())

main.py

#!/usr/bin/env python3
import sys

def main(argv=None):
    if argv is None:
        argv = sys.argv

    print("Hello, world")

    return 0

Go in the terminal to the package_name folder and type: "python3 package_name.py" to execute the code.

Output

Hello, world

The package.py goes to the main.py and execute the code that is in the main.py. If you want to import in your example try using for example "from package_name.A.py import [function name]" in the the python files you wish to access the functions. It should work.

I looked at: https://stackoverflow.com/questions/9882447/cython-importerror-no-module-named-mymodule-how-to-call-a-cython-module-con and it seemed to explain too — Hyrial, Jul 04 '19 at 06:14

How to correctly make a python package?

1 Answers1