How to Retrieve Subclasses of a Class by Name in Python?

Finding Subclasses of a Class by Name in Python

Problem:
How can you retrieve all classes that inherit from a given base class in Python, using its class name?

Solution:

Python offers an elegant approach for finding subclasses of a specified class by its name. Through the __subclasses__ method, you can directly retrieve the subclasses of a class.

Code Explanation:

Assuming you have a base class named Foo with subclasses Bar, Baz, and Bing, the following code snippet illustrates the usage of __subclasses__:

class Foo(object):
    pass

class Bar(Foo):
    pass

class Baz(Foo):
    pass

class Bing(Bar):
    pass

# Get the subclasses of Foo
foo_subclasses = Foo.__subclasses__()
print("Subclass names:", [cls.__name__ for cls in foo_subclasses])
print("Subclasses themselves:", Foo.__subclasses__())

# Validate that the subclasses inherit from Foo
for cls in Foo.__subclasses__():
    print("Base class of {}: {}".format(cls, cls.__base__))

Output:

Subclass names: ['Bar', 'Baz']
Subclasses themselves: [<class '__main__.Bar'>, <class '__main__.Baz'>]
Base class of <class '__main__.Bar'>: <class '__main__.Foo'>
Base class of <class '__main__.Baz'>: <class '__main__.Foo'>

Finding Sub-subclasses:
If you need to find sub-subclasses, you can use a recursive function:

def all_subclasses(cls):
    return set(cls.__subclasses__()).union(
        [s for c in cls.__subclasses__() for s in all_subclasses(c)])

Note:
It's crucial to note that for __subclasses__ to work effectively, the class definitions of the subclasses must have been executed previously. If you have a string representing the class name, you can first retrieve the class using techniques like globals(), locals(), or importlib.

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