CODEWITHSUNDEEP
pythonpython-3.xclassdictionarysubclassing
Ma0
Ma0

Reputation: 15204

Overwritting dictionary 'update' method

I am trying to subclass dict to modify its update method.

The behavior I am looking for is to add the values of common keys and keep the unique ones.

Example:

g1 = MyDict({1: 1, 2: 2})
g2 = MyDict({1: 1, 3: 3})
g1.update(g2)  # should result in g1 = {1: 2, 2: 2, 3: 3}
#                                          ^ because it is 1 from g1 + 1 from g2

in other words, as if I was doing:

from collections import Counter
g1 =  dict(Counter(g1) + Counter(g2))

For this task, I wrote the following:

class MyDict(dict):
    def __update__(self, d2):
        keys = set(self).union(d2)
        self = {k: self.get(k, 0) + d2.get(k, 0) for k in keys}
        return

but when doing:

g1 = MyDict({1: 1, 2: 2})
g2 = MyDict({1: 1, 3: 3})
g1.update(g2)

it produces:

{1: 1, 2: 2, 3: 3}

However, if I do:

class MyDict(dict):
    def __add__(self, d2):
        keys = set(self).union(d2)
        return {k: self.get(k, 0) + d2.get(k, 0) for k in keys}

and then

g1 = g1 + g2

the desired behavior is implemented..

What am I doing wrong when overwriting the update method?

Upvotes: 2

Views: 73

Answers (1)

Ma0
Ma0

Reputation: 15204

I found the following way to do it:

class MyDict(dict):
    def update(self, d2):
        for k in set(self).union(d2):
            self[k] = self.get(k, 0) + d2.get(k, 0)
        return

which indeed, when doing:

g1 = MyDict({1: 1, 2: 2})
g2 = MyDict({1: 1, 3: 3})
g1.update(g2)

results in:

print(g1)  # -> {1: 2, 2: 2, 3: 3}

If there is a better way, let me know.

Thanks for the comments!

Upvotes: 3

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