Python - Dynamic class import

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?

Sorry - it is not possible to figure out what you want - your pseudocode is unclear. Python does take care of abse classes coming from the right places, howeer. So that Any App1.Class_ will see "Producer" as it is defined inside the App1 module. — jsbueno, Nov 09 '11 at 16:58
Sorry, I tried to be as clear as possible. I have edited to the post and hope it makes more sense. — Hanpan, Nov 09 '11 at 17:04

score 5 · Accepted Answer · edited May 23 '17 at 12:33

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.

Python - Dynamic class import

1 Answers1