How to Build a Two-Way Dictionary in Python

class BiDict:
    def __init__(self, data=None):
        self.forward = {}
        self.backward = {}
        if data:
            self.update(data)

    def update(self, data):
        for key, value in data.items():
            self[key] = value

    def __setitem__(self, key, value):
        self.forward[key] = value
        self.backward[value] = key

    def __getitem__(self, key):
        return self.forward[key]

    def get_key(self, value):
        return self.backward[value]

    def __delitem__(self, key):
        value = self.forward.pop(key)
        del self.backward[value]

    def __len__(self):
        return len(self.forward)

    def __repr__(self):
        return f"BiDict({self.forward!r})"

if __name__ == "__main__":
    bd = BiDict({"apple": "fruit", "carrot": "vegetable"})
    print("Forward:", bd["apple"])
    print("Backward:", bd.get_key("vegetable"))
    bd["banana"] = "fruit"
    print("After add:", bd)
    del bd["carrot"]
    print("After delete:", bd)
    print("Size:", len(bd))