https://stackoverflow.com/questions/4162456/forward-declaration-of-classes?rq=1
class Base:
pass
# subs = [Sub3,Sub1]
# Note that this is NOT a list of all subclasses!
# Order is also important
class Sub1(Base): pass
class Sub2(Base): pass
class Sub3(Base): pass
class Base(object): # New-style class (i.e. explicitly derived from object).
@classmethod
def register_subclass(cls, subclass):
""" Class decorator for registering subclasses. """
# Replace any occurrences of the class name in the class' subs list.
# with the class itself.
# Assumes the classes in the list are all subclasses of this one.
# Works because class decorators are called *after* the decorated class'
# initial creation.
while subclass.__name__ in cls.subs:
cls.subs[cls.subs.index(subclass.__name__)] = subclass
return cls # Return modified class.
subs = ['Sub3', 'Sub1'] # Ordered list of subclass names.
@Base.register_subclass
class Sub1(Base): pass