I am trying to use an object as the key value to a dictionary in Python. I follow the recommendations from some other posts that we need to implement 2 functions: __hash__ and __eq__

And with that, I am expecting the following to work but it didn't.

class Test:def __init__(self, name):self.name = namedef __hash__(self):return hash(str(self.name))def __eq__(self, other):return str(self.name) == str(other,name)def TestMethod():test_Dict = {}obj = Test('abc')test_Dict[obj] = objprint "%s" %(test_Dict[hash(str('abc'))].name)       # expecting this to print "abc" 

But it is giving me a key error message:

KeyError: 1453079729188098211

You don't need to redefine hash and eq to use an object as dictionary key.

class Test:def __init__(self, name):self.name = nametest_Dict = {}obj = Test('abc')
test_Dict[obj] = objprint test_Dict[obj].name

This works fine and print abc. As explained by Ignacio Vazquez-Abrams you don't use the hash of the object but the object itself as key to access the dictionary value.

The examples you found like python: my classes as dict keys. how? or Object of custom type as dictionary key redefine hash and eq for specific purpose.

For example consider these two objects obj = Test('abc') and obj2 = Test('abc').

test_Dict[obj] = obj
print test_Dict[obj2].name

This will throw a KeyError exception because obj and obj2 are not the same object.

class Test:def __init__(self, name):self.name = namedef __hash__(self):return hash(str(self.name))def __eq__(self, other):return str(self.name) == str(other.name)obj = Test('abc')
obj2 = Test('abc')       test_Dict[obj] = obj
print test_Dict[obj2].name

This print abc. obj and obj2 are still different objects but now they have the same hash and are evaluated as equals when compared.