CODEWITHSUNDEEP
pythondictionaryhash
Luca
Luca

Reputation: 10996

__eq__ implementation for hashing of multiple types

I have a custom class which I want to be able to use as a key in a dictionary. So, I need to define the __eq__ function. In my case, this is simple:

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

Here other needs to be basically of the same type and I am comparing some member variables. However, the name is just a string and what I was thinking was that the user could also check by specifying a string. To make it concrete, here is what I had in mind:

class Hashable(object):
    def __init__(self, name):
        self.name = name
        self.other_att = dict()

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

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

# Example usage
from collections import defaultdict

c = defaultdict()
h = Hashable("Name")
c[h] = list()
if h in c:
    print ("Yes!")   # This is fine...

However, also want to do:

if 'Name' in c:

Can I implement many __eq__ functions or do I need to check for the type of other in the equality function. What is a pythonic an hopefully efficient way to do this?

Upvotes: 0

Views: 120

Answers (2)

Kasravnd
Kasravnd

Reputation: 107297

You can just use a try-except, because sometimes it's easier to ask for forgiveness than permission:

def __eq__(self, other):
    try:
        return self.name == other.name
    except AttributeError:
        return self.name == other

Upvotes: 2

Moses Koledoye
Moses Koledoye

Reputation: 78554

Use getattr and provide the default as other in case other has no attribute name e.g. it's a string:

def __eq__(self, other):
    return self.name == getattr(other, 'name', other)

Upvotes: 2

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