How Can I Find All Subclasses of a Python Class?

Accessing Subclasses of a Class

In Python, finding all subclasses of a given class can be achieved through the __subclasses__ method. This method is available for new-style classes (those inheriting from object in Python 3 or subclassed from a new-style class).

For example, consider the following code:

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

To retrieve the subclasses of Foo, we can use the following code:

print([cls.__name__ for cls in Foo.__subclasses__()])

This will print the names of the subclasses:

['Bar', 'Baz']

We can also obtain the subclasses themselves using __subclasses__():

print(Foo.__subclasses__())

This will print the following list of subclasses:

[<class>, <class>]</class></class>

To confirm that these subclasses indeed have Foo as their base class, we can use the following code:

for cls in Foo.__subclasses__():
    print(cls.__base__)

This will print the following:

<class>
<class></class></class>

However, it should be noted that if the class definition of a subclass has not yet been executed, it will not be found by __subclasses__. To account for this, recursion can be employed:

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

print(all_subclasses(Foo))

This will print:

{<class>, <class>, <class>}</class></class></class>

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