zwadar/module_inheritance

Module Inheritance Package

Package to allow overriding python packages in a similar manner as class subclassing works. Probably it won't find much use on normal usage scenario. However, it might be very useful in scenarios where one Python code is supposed to run inside multiple different applications embedding Python.

The override process is automatic and happens on the folder structure. So the main code does not need to be aware of the override process. Also, it overrides individual members, and not the whole module. So the override files don't need to contain all content from the original module.

Usage

Simple

Lets have a module my_module.py

def get_python_interpreter():
    return "python.exe"
    
def get_number():
    return 42

and then client code

import os
import my_module

os.system(my_module.get_python_interpreter())
print(my_module.get_number())

However, some applications while embedding Python, have unique names of their interpreter so the code won't work. To make the client working across all environments. We first need to create to override module at some path e.g. my_overrides/my_module.py

def get_python_interpreter():
    return "custom_intepreter_name.exe"

and then register to root folder into the system in some application initialisation sequence

import module_inheritance

module_inheritance.register_path("my_overrides")

This setup will hijack the import machinery, and will cause the get_python_interpreter to return new interpreter name, but the get_number method will still return 42.

Hierarchy

The system is not limited to just one override, and it is possible to register multiple paths.

import module_inheritance

module_inheritance.register_path("my_overrides")
module_inheritance.register_path("my_another_overrides")
module_inheritance.register_path("my_yet_another_overrides")

Most recent overrides are then picked.

Using parent and base

With the hierarchy in place, it is also possible to call original overriden methods, the same way super is working in the class subclassing. So for file my_yet_another_overrides/my_module.py we can do

import module_inheritance

def get_number():
    return module_inheritance.parent.get_number() * 2

module_inheritance.parent refers to the closest version of the method in the override hierarchy, on the other hand module_inheritance.base refers to the original, unmodified root module.

Overriding Classes

With the base and parent member, it is also possible to create override classes by simply subclassing from them and using the same name. This allows full customisation of the classes in the override code without any need to change the client code.

Let's define new class in my_module.py

class MyClass(object):
    
    def __init__(self):
        pass
    
    def do_it(self):
        return 8

and then create override in the my_overrides/my_module.py

import module_inheritance

class MyClass(module_inheritance.parent.MyClass):
    
    def do_it(self):
        return super() * 2