Python (and me) getting confused finding keys

[Gabriel Genellina]

En Tue, 22 Dec 2009 13:56:36 -0300, John <john at nurfuerspam.de> escribió:

>> another thread can remove the key prior to the has_key call; or perhaps
>>  edges isn't a real dictionary?
>>
>
> of course. But unless there is a way of using threading without being  
> aware of
> it, this is not the case. Also, edges is definitely a dict (has been  
> declared
> some lines before, and no obscure functions have been called in the  
> meantime,
> just some adding to edges). Python would also fail on edges.keys() if  
> edges
> wasn't a dict...

Ok, then your edges are mutable:

py> class Edge:
...   def __init__(self, x):
...     self.x = x
...   def __eq__(self, other):
...     return self.x==other.x
...   def __hash__(self):
...     return hash(self.x)
...
py> e1 = Edge(1)
py> e2 = Edge(2)
py> e3 = Edge(3)
py> edges = {e1:None, e2:None, e3:None}
py> e2.x = 5
py> for e in edges.keys():
...   assert edges.has_key(e)
...
Traceback (most recent call last):
   File "<stdin>", line 2, in <module>
AssertionError
py> for e in edges:
...   assert e in edges
...
Traceback (most recent call last):
   File "<stdin>", line 2, in <module>
AssertionError

Once you compute an object's hash, it must remain immutable. Is this your  
problem?

-- 
Gabriel Genellina