Enabling delegation / prototypal inheritance / instance based programming in Python

proto-demo.py

from proto import Proto, ProtoMeta
__metaclass__ = ProtoMeta

class A:
  x = "This is X"
  def getY(self):
    return self._y

class B:
  _y = "This is Y"

if __name__ == "__main__":
  a = A(None)
  b = B(a)
  print b.x
  print b.getY()

proto-demo2.py

from proto import Proto, ProtoMeta

class A(Proto):
  x = "This is X"
  def getY(self):
    return self._y

class B(Proto):
  _y = "This is Y"

class C(object):
  def __getattr__(self, name):
    return "So you want "+name

class D(B,C):
  pass

if __name__ == "__main__":
  a = A(None)
  b = B(a)
  print b.x
  print b.getY()
  d = D(a)
  print d.x
  print d.getY()
  print d.z

proto.py

import types
import inspect

class Proto(object):
  def __new__(self, proto, *args, **kw):
    return super(Proto, self).__new__(self, *args, **kw)
  def __init__(self, proto, *args, **kw):
    self.proto = proto
    super(Proto, self).__init__(*args, **kw)
  def __getattr__(self, name):
    try:
      attr = getattr(self.proto, name)
      if (inspect.ismethod(attr) and attr.__self__ is self.proto):
        attr = types.MethodType(attr.__func__, self)
      return attr
    except AttributeError:
      return super(Proto, self).__getattr__(name)


class ProtoMeta(type):
  def __new__(self, name, bases, dict):
    return super(ProtoMeta, self).__new__(self, name, (Proto,) + bases, dict)
  def __init__(self, name, bases, dict):
    super(ProtoMeta, self).__init__(name, (Proto,) + bases, dict)