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Here is my code:
class Hero: def __init__(self, name, age): self.name = name self.age = age def __str__(self): return self.name + str(self.age) def __hash__(self): print(hash(str(self))) return hash(str(self)) heroes = set() heroes.add(Hero('Zina Portnova', 16)) # gets hash -8926039986155829407 print(len(heroes)) # gets 1 heroes.add(Hero('Lara Miheenko', 17)) # gets hash -2822451113328084695 print(len(heroes)) # gets 2 heroes.add(Hero('Zina Portnova', 16)) # gets hash -8926039986155829407 print(len(heroes)) # gets 3! WHY? Why is this happening?
The 1st and the 3rd object have same content and same hash but len() tells about 3 unique objects?
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An object hash is an integer number representing the value of the object and can be obtained using the hash() function if the object is hashable. To make a class hashable, it has to implement both the __hash__(self) method and the aforementioned __eq__(self, other) method. As with equality, the inherited object.
An object is said to be hashable if it has a hash value that remains the same during its lifetime.
Hashable. 00:00 Immutable objects are a type of object that cannot be modified after they were created. Hashable objects, on the other hand, are a type of object that you can call hash() on.
Hashable data types: int , float , str , tuple , and NoneType . Unhashable data types: dict , list , and set .
You also need to define __eq__() in a compatible way with __hash__() – otherwise, equality will be based on object identity.
On Python 2, it is recommended you also define __ne__ to make != consistent with ==. On Python 3, the default __ne__ implementation will delegate to __eq__ for you.
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