class Outer(object):
class Inner(object):
def __init__(self, outer):
self.outer = outer
import new
Outer.Inner = new.instancemethod(Outer.Inner, None, Outer)
# That's it. Now you cannot create an Inner without an Outer.
# For a more self-contained solution using metaclasses:
def hasinnerclasses(classname, bases, d):
import new, types
klass = new.classobj(classname, bases, d)
for name,cls in d.items():
if isinstance(cls, (type, types.ClassType)):
setattr(klass, name, new.instancemethod(cls, None, klass))
return klass
class Outer(object):
__metaclass__ = hasinnerclasses
class Inner(object):
def __init__(self, outer):
self.outer = outer
>>> out = Outer()
>>> inr = out.Inner() # Note that *both* arguments are supplied automatically
>>> inr.outer is out
True
# Trying to cheat doesn't work...
>>> cheat = Outer.Inner() #fails
>>> cheat = Outer.Inner('foo') #also fails
