How can I find the subclasses of a given class in Python?

Finding Subclasses of a Class in Python

In Python, you can determine the subclasses of a given class through its __subclasses__() method. This method is available to new-style classes, which are inherited from the "object" class and are commonly used in Python 3.

To obtain the names of the subclasses:

class Foo(object): pass
class Bar(Foo): pass
class Baz(Foo): pass
class Bing(Bar): pass

[cls.__name__ for cls in Foo.__subclasses__()]
# ['Bar', 'Baz']

Alternatively, to retrieve the subclasses themselves:

Foo.__subclasses__()
# [<class '__main__.Bar'>, <class '__main__.Baz'>]

To confirm the base class association:

for cls in Foo.__subclasses__():
    print(cls.__base__)
# <class '__main__.Foo'>
# <class '__main__.Foo'>

Recursive Subclass Retrieval:

If you need to capture subsubclasses (grandchildren, etc.), a recursive approach is necessary:

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

all_subclasses(Foo)
# {<class '__main__.Bar'>, <class '__main__.Baz'>, <class '__main__.Bing'>}

Note: If a subclass's class definition has not been executed (e.g., its module is not imported), it won't be detectable by __subclasses__().

Obtaining Subclasses from a Class Name:

Suppose you have the class name as a string instead. In that case, follow these steps:

1. Find the class object using the class name:

   • If in the same module:

     cls = globals()[name]

   • If in any module:

     import importlib
     modname, _, clsname = name.rpartition('.')
     mod = importlib.import_module(modname)
     cls = getattr(mod, clsname)

2. Use __subclasses__() to obtain the subclasses of the retrieved class object.

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