如何在Python中找到一個類別的所有子類別？

Finding All Subclasses of a Class in Python

To retrieve all classes inherited from a specified base class in Python, utilize the __subclasses__() method. This method is available for new-style classes that extend the object class (the default in Python 3). Here's how it works:

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

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

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

To include subsubclasses, recursion can be used:

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

Note: Subclasses that have not been defined yet (e.g., due to unimported modules) will not be detected by __subclasses__().

Locating Subclasses Using a Class Name String:

When only the class name is available as a string, the following steps are necessary:

1. Find the class using the class name.
2. Utilize __subclasses__() to retrieve the subclasses of the located class.

Finding a Class from a Name String:

The method for locating a class from a name string depends on its expected location:

• If expected within the same module:

  cls = globals()[name]

• If expected within the locals namespace:

  cls = locals()[name]

• If anywhere in the modules:

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

Once the class is found, its __subclasses__() method can be used to retrieve the desired list of subclasses.

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