class Node:
    def __init__(self, *args):
        self.args = args
    def __repr__(self):
        return str(self.args)

class List(Node):
    pass

class Union(Node):
    pass

class Dict(Node):
    pass

def iter_concrete_types(obj):
    if isinstance(obj, Union):
        for arg in obj.args:
            yield from iter_concrete_types(arg)
    elif isinstance(obj, List):
        for arg in obj.args:
            for t in iter_concrete_types(arg):
                yield f"List[{t}]"
    elif isinstance(obj, Dict):
        k,v = obj.args
        for tk in iter_concrete_types(k):
            for tv in iter_concrete_types(v):
                yield f"Dict[{tk}, {tv}]"
    elif isinstance(obj, type):
        yield obj.__name__
    else:
        raise Exception(f"Don't know how to concretize object of type {type(obj)}")

x = Union(List(Union(Dict(str, Union(int, List(int))), Dict(str, Union(Dict(str, Union(int, List(int))), List(int))))), Union(Dict(str, Union(int, List(int))), Dict(str, Union(Dict(str, Union(int, List(int))), List(int)))))

for t in iter_concrete_types(x):
    print(t)

"""result:
List[Dict[str, int]]
List[Dict[str, List[int]]]
List[Dict[str, Dict[str, int]]]
List[Dict[str, Dict[str, List[int]]]]
List[Dict[str, List[int]]]
Dict[str, int]
Dict[str, List[int]]
Dict[str, Dict[str, int]]
Dict[str, Dict[str, List[int]]]
Dict[str, List[int]]
"""