Object equallity in python collections.Counter

counter, dictionary, object-equality, python

Solution

You also have to implement `__hash__`:

class Person(object):
    def __init__(self, name=None, address=None):
        self.name = name
        self.address = address

    def __eq__(self, other):
        return self.name == other.name and self.address == other.address

    def __hash__(self):
        return hash((self.name, self.address))

Now your code works:

>>> Counter(people)
Counter({<__main__.Person object at 0x24a7590>: 2, <__main__.Person object at 0x24a75d0>: 1})

Problem

I have and instance of collections.Counter class, also i have some objects like: ``` p1 = Person(name='John') p2 = Person(name='John') p3 = Person(name='Jane') ``` I want to hold the counts for this person objects in a instance of Counter, taking into account that person objects with same names must increment the same person count, so if i have a list with all person objects: ``` people = [p1, p2, p3] ``` and i populate my counter with it: ``` c = Counter(people) ``` i want to get the following: ``` c[p1] #prints 2 c[p2] #prints 2 c[p3] #prints 1 ``` My first attempt was to implement a new `__eq__` method for person objects ``` def __eq__(self, other): return self.name == other.name ``` I thought that this could work because counter objects seems like increment the counts for keys based on the equality of the key objects, like in: ``` c = Counter(['A', 'A', 'B']) c['A'] #prints 2 c['B'] #prints 1 ``` Another attempt could be inherit from Counter and override the underlying method that Counter uses for measure the equality between objects , i am not sure but i think Counter uses `__contains__` method for that. My question is if there are any way to gets this behavior without using inheritance and if not, what could be the best way to do it?.

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