On Python Classes and introspection¶

Find out if a class is a subclass¶

In [1]:

class Upper(object):
    def __init__(self):
        pass

class Lower(Upper):
    def __init__(self):
        Upper.__init__(self)
        self.type = type(self)

issubclass(Lower, Upper)

Out[1]:

True

Subclasses can know that they are subclasses¶

In [2]:

class Upper(object):
    def __init__(self):
        pass

class Lower(Upper):
    def __init__(self):
        Upper.__init__(self)
        self.type = type(self)
        self.issub = issubclass(self.type, Upper)

u = Upper()
l = Lower()
print(l.type)
print(l.issub)

<class '__main__.Lower'>
True

Subclasses of subclasses can know their parent and grandparent classes¶

In [3]:

class MoreLower(Lower):
    def __init__(self):
        Lower.__init__(self)
        self.type = type(self)
        self.issub = issubclass(self.type, Lower)
        self.issubsub = issubclass(self.type, Upper)


m = MoreLower()
print(m.type)
print(m.issub)
print(m.issubsub)

<class '__main__.MoreLower'>
True
True

In [4]:

MoreLower.__base__

Out[4]:

__main__.Lower

In [5]:

Upper.__base__

Out[5]:

object

Stckoverflow: How can I find all subclasses of a class given its name?¶

In [6]:

class Foo(object):
    pass

class Bar(Foo):
    pass

class Baz(Foo):
    pass

class Bing(Bar):
    pass

In [7]:

#Here are the names of the subclasses:

Foo.__subclasses__()

Out[7]:

[__main__.Bar, __main__.Baz]

In [8]:

# Confirmation that the subclasses do indeed list Foo as their base:

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

<class '__main__.Foo'>
<class '__main__.Foo'>

In [9]:

# Note if you want subsubclasses, you'll have to recurse:

def all_subclasses(cls):
    return cls.__subclasses__() + [g for s in cls.__subclasses__()
                                   for g in all_subclasses(s)]

print(all_subclasses(Foo))

[<class '__main__.Bar'>, <class '__main__.Baz'>, <class '__main__.Bing'>]