this post was submitted on 26 Feb 2025
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Python

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class Node:
    def __init__(self, edges = set()):
        self.edges = edges


def main():
    foo = Node()
    bar = Node()
    quz = Node()

    foo.edges.add(bar)
    bar.edges.add(foo)

    assert(foo is not bar) # assertion succeeds
    assert(foo is not quz) # assertion succeeds
    assert(bar is not quz) # assertion succeeds
    assert(len(quz.edges) == 0) # assertion fails??


main()

spoilerMutable default values are shared across objects. The set in this case.

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[โ€“] [email protected] 4 points 5 days ago (1 children)

You may like collections.defaultdict. Pass the constructor a factory function to be run when a key is missing.

dd = defaultdict(list)
dd['key'].append("value")
print(dd['key'])  # ["value"]
[โ€“] technohacker 1 points 5 days ago

Ah sorry I meant a default argument which was a dict, thanks for the tip tho!