How to find all the subclasses of a class given its name?

Question

I need a working approach of getting all classes that are inherited from a base class in Python.

Answer 1

This isn't as good an answer as using the special built-in __subclasses__() class method which @unutbu mentions, so I present it merely as an exercise. The subclasses() function defined returns a dictionary which maps all the subclass names to the subclasses themselves.

def traced_subclass(baseclass):
    class _SubclassTracer(type):
        def __new__(cls, classname, bases, classdict):
            obj = type(classname, bases, classdict)
            if baseclass in bases: # sanity check
                attrname = '_%s__derived' % baseclass.__name__
                derived = getattr(baseclass, attrname, {})
                derived.update( {classname:obj} )
                setattr(baseclass, attrname, derived)
             return obj
    return _SubclassTracer

def subclasses(baseclass):
    attrname = '_%s__derived' % baseclass.__name__
    return getattr(baseclass, attrname, None)


class BaseClass(object):
    pass

class SubclassA(BaseClass):
    __metaclass__ = traced_subclass(BaseClass)

class SubclassB(BaseClass):
    __metaclass__ = traced_subclass(BaseClass)

print subclasses(BaseClass)

Output:

{'SubclassB': ,
 'SubclassA': }