A dataclass as a key to a defaultdict: KeyError
Solution 1:
collections.defaultdict(default_factory=int) creates a default dict with no default value type, and one value (the type int at the key "default_factory") because default_factory can only be passed as positional argument. Any keyword arguments are considered key-value pairs for the dictionary:
defaultdict(None, {'default_factory': int})
You need to do collections.defaultdict(int), which produces defaultdict(int, {})