insert unique data in a list

[Lie Ryan]

On 12/15/2009 4:13 AM, mattia wrote:
>> >
>> >  of course it is broken as long as it uses it's instance id. i added this
>> >  to notify that unhashable can become hashable implementing __hash__
>> >  inside the class. which probably set to None by default.
> Ok, nice example, but I believe that using id() as the hash function can
> lead to unexpected collisions.

For dict and set to work correctly, the hash function must conform to 
the contract that:
- if A == B then hash(A) == hash(B)

If the id() of two objects differ but their content equal (i.e. they are 
two equivalent, but distinct object), they should have the same hash. If 
id() is used for the hash of an arbitrary object, the contract will be 
broken unless you define A == B in terms of id(A) == id(B).