question is when i import a dict , i think it is a global var, but python seem create a new dict，they have different id. i can not understand

there are two file named main.py and add_cache.py

# main.py
d = {}
if __name__ == '__main__':

    from add_cache import AddDictTest
    AddDictTest.add_to_dict("a")
    AddDictTest.add_to_dict("b")
    print("d id is ", id(d))
    print(d)

#add_cache.py
class AddDictTest(object):
    @classmethod
    def add_to_dict(cls, key):
        from main import d
        tt = d.setdefault(key, {})
        tt["b"] = "b"
        print("d id is ", id(d))

when i run main.py

#output is 
d id is  2175240751296
d id is  2175240751296
d id is  2175238904384
{}

in my understand , d is not be empty, and there id should same.

I want to konw why create a new empty dict when import , I have ask gpt, it give a answer about cycle import. but i still can not understand deep reason.