class Collection():
    def __init__(self, db):
        self.x = db

    def printDbName(self):
        print self.x

parent = Collection('hkpr')

parent.printDbName()

class Document(Collection):
    def __init__(self, db):
        self.db = db
        Collection.__init__(self, self.db)

    def printChild(self):
        print self.x

child = Document('yabba')
child.printChild()
child.printDbName()