pythondictionaryargument-unpacking

Is Python dictionary unpacking customizable?

Is there a dunder method which corresponds to using the dictionary unpacking opertator ** on an object?

For example:

class Foo():
    def __some_dunder__(self):
        return {'a': 1, 'b': 2}

foo = Foo()
assert {'a': 1, 'b': 2} == {**foo}
Solution

  • I've managed to satisfy the constraint with two methods (Python 3.9) __getitem__ and keys():

    class Foo:
    def __getitem__(self, k): # <-- obviously, this is dummy implementation
        if k == "a":
            return 1

        if k == "b":
            return 2

    def keys(self):
        return ("a", "b")


foo = Foo()
assert {"a": 1, "b": 2} == {**foo}

    For more complete solution you can subclass from collections.abc.Mapping (Needs implementing 3 methods __getitem__, __iter__, __len__)