Converting object to dictionary key

user_6692319 0
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I was wondering if there is an easy way to essentially have multiple keys in a dictionary for one value. An example of what I would like to achieve is as following:

class test:
    key="test_key"
    
    def __str__(self):
        return self.key

tester = test()

dictionary = {}
dictionary[tester] = 1

print(dictionary[tester])
print(dictionary["test_key"])

where the output would be:

>>> 1
>>> 1

What I'm looking for is a way to automatically convert the object to a string before its used as a key. Is this possible?

hashmap object dictionary python string
2 Answers

Personally, I think it's better to explicitly cast the object to a string, e.g.

dictionary[str(tester)] = 1

That being said, if you're really really REALLY sure you want to do this, define the __hash__ and __eq__ dunder methods. No need to create a new data structure or change the existing code outside of the class definition:

class test:
    key="test_key"
    
    def __hash__(self):
        return hash(self.key)
        
    def __eq__(self, other):
        if isinstance(other, str):
            return self.key == other
        return self.key == other.key
    
    def __str__(self):
        return self.key

This will output:

1
1
user_177698150

It is almost certain you should not do this; just use dictionary[str(tester)]. It is more readable, less surprises, only five characters more to write.

If you insist though, this is the best I can think of

class StrKeyedDict(dict):
    def __getitem__(self, key):
        return super().__getitem__(str(key))
    def __setitem__(self, key, value):
        super().__setitem__(str(key), value)
    # ... do all the other methods that mess with the key

class Test:
    key="test_key"

    def __str__(self):
        return self.key

tester = Test()
dictionary = StrKeyedDict()
dictionary[tester] = 1
print(dictionary["test_key"])
# => 1
user_2404430
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