Import class dynamically

[voltron]

I have two base classes FirstBaseClass and SecondBaseClass and lot of theirs subclasses. Each subclass defined in the separate file, location of these files is known. I need to import and instantiate subclasses programmatically. Now I use following approach:

import inspect
import importlib

class_name = "FirstChildClass"
file_path = "/path/to/class.py"

try:
    spec = importlib.util.spec_from_file_location(class_name, file_path)
    module = importlib.util.module_from_spec(spec)
    spec.loader.exec_module(module)
    for x in dir(module):
        obj = getattr(module, x)
        if inspect.isclass(obj) and (issubclass(obj, FirstBaseClass) or issubclass(obj, SecondBaseClass)) and obj.__name__ == class_name:
            return obj()
except ImportError as e:
    print(e)    

But problem is that I need to know class name. Is it possible to import class from file without knowing its name, assuming that only one class defined in that file?