Python - Get class of type from imported module

Question

I am trying to import a class from a file with a dynamic name. Here is my file importer:

def get_channel_module(app, method):
    mod_name = 'channel.%s.%s' % (app, method)
    module = __import__(mod_name, globals(), locals(), [method])
    return module

This imports the specific python file, for example, some_file.py, which looks like this:

class SomeClassA(BaseClass):
    def __init__(self, *args, **kwargs):
        return

class SomeClassB():
    def __init__(self, *args, **kwargs):
        return

What I want to do is return only the class which extends BaseClass from the imported file, so in this instance, SomeClassA. Is there any way to do this?

Ferdinand Beyer · Accepted Answer · 2011-05-23 09:30:27Z

8

You can do this by inspecting the symbols in your module with issubclass:

def get_subclass(module, base_class):
    for name in dir(module):
        obj = getattr(module, name)
        try:
            if issubclass(obj, base_class):
                return obj
        except TypeError:  # If 'obj' is not a class
            pass
    return None

answered May 23, 2011 at 9:30

Ferdinand Beyer

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Comments

Rob Cowie · Accepted Answer · 2011-05-23 09:33:11Z

4

Once you have your module imported, iterate it's namespace looking for class objects that are subclasses of BaseClass.

klasses = [c for c in module.__dict__.values() if isinstance(c, type)]
base_subclasses = [c for c in klasses if issubclass(c, BaseClass]
## or as a single list comprehension
base_subclasses = [c for c in module.__dict__.values() if isinstance(c, type) and issubclass(c, BaseClass)]

answered May 23, 2011 at 9:33

Rob Cowie

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2 Comments

Rob Cowie Over a year ago

Which is basically the same as the answer provided by @Ferdinand Beyer

Pekka Klärck Over a year ago

isinstance(c, type) does not work with old style classes. Should use inspect.isclass(c) instead. Or perhaps even klasses = inspect.getmembers(module, inspect.isclass).

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