Raymond Hettinger added the comment:
> 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.
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