Question

I have the following folder structure:

- MyProject
    - App1
        - some_module1.py
        - some_module2.py
    - App2
        - some_other_module1.py
        - some_other_module2.py

Inside each of the modules (some_module1.py for example) there is a class that extends from a base class, in my case, Producer.

What I am trying to do is dynamically load in this class. To do that, I have a list of “installed apps” that looks like this:

INSTALLED_APPS = (
    'App1',
    'App2',
)

I am trying to write a function that will check each “app” package for a particular producer class and ensure it extends from the producer base class. Something like this:

module_class = 'some_module1.SomeClass'

# Loop through each package in the INSTALLED_APPS tuple:
for app in INSTALL_APPS:
    try:
        #is the module_class found in this app?
        #App1.some_module1.SomeClass - Yes
        #App2.some_module1.SomeClass - No

        # is the class we found a subclass of Producer?
    exception ImportError:
        pass

I’ve tried experimenting with imp and importlib, but it doesn’t seem to handle this kind of import. Is there anyway for me to be able to achieve this?

Answer 1

You may want to have a look at:

• __import__() to import modules knowing their name as string;
• dir() to get the names of all the objects of a module (attributes, functions, etc);
• inspect.isclass(getattr(<module ref>, <object name>)) to identify classes among the objects of a module;
• issubclass() to identify sub-classes from a given class, as explained here.

With these tools, you can identify all classes in a given module, that are inheriting a given class.

I’m using this mechanism to dynamically instantiate classes from given module, so that their updates are automatically taken into account at an upper level.