homepage

> This is a consequence of subclassing a builtin type
Not really. This is how subclassing works in general. Any time you a user calls a parent class directly on an instance of subclass, they are bypassing whatever the subclass needs to do to maintain its invariants.
class A:
 def __init__(self):
 self.data = []
 def add(self, x):
 self.data.append(x)
class B(A):
 'Track the number of odds'
 def __init__(self):
 A.__init__(self)
 self.odds = 0
 def add(self, x):
 A.add(self, x)
 self.odds += (x % 2)
b = B()
b.add(1)
b.add(2)
b.add(3)
b.add(4)
A.add(b, 5)
assert b.odds == sum(x%1 for x in b.data), 'OMG, B is broken!'
There is nothing special about OrderedDicts in this regard. Perhaps there should be a FAQ entry regarding the "facts of life" in the world of object oriented programming.