# -*- coding: utf-8 -*-
from zope.interface import Interface
from zope.interface import implementer
from zope import schema


class IContainer(Interface):

    parent = schema.Object(
        title=u'Parent container',
        schema=IContainer,  # How can I do this, IContainer is not yet defined.
        required=False,
        default=None,
    )


@implementer(IContainer)
class Container(object):

    parent = schema.fieldproperty.FieldProperty(IContainer['parent'])

    def __init__(self, parent=None):
        self.parent = parent


c1 = Container()
c2 = Container(parent=c1)