Building a Bidirectional Dictionary (Two-Way Map)

class BidirectionalDict:
    def __init__(self, initial_dict=None):
        self._forward = {}
        self._backward = {}
        if initial_dict:
            for key, value in initial_dict.items():
                self[key] = value

    def __setitem__(self, key, value):
        # Ensure consistency: if the key or value already exists, remove old mappings
        if key in self._forward:
            old_value = self._forward[key]
            del self._backward[old_value]
        if value in self._backward:
            old_key = self._backward[value]
            del self._forward[old_key]

        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 get(self, key, default=None):
        return self._forward.get(key, default)

    def get_key_safe(self, value, default=None):
        return self._backward.get(value, default)

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

    def __contains__(self, key):
        return key in self._forward

    def contains_value(self, value):
        return value in self._backward

    def __delitem__(self, key):
        value = self._forward[key]
        del self._forward[key]
        del self._backward[value]

    def __repr__(self):
        return f"BidirectionalDict({self._forward})"

# Example Usage:
id_to_name = BidirectionalDict({'user1': 'Alice', 'user2': 'Bob'})
print(f"Initial map: {id_to_name}")

id_to_name['user3'] = 'Charlie'
print(f"After adding 'user3': {id_to_name}")

print(f"Name for user1: {id_to_name['user1']}")
print(f"ID for Alice: {id_to_name.get_key('Alice')}")

# Overwriting a key
id_to_name['user1'] = 'Alicia'
print(f"After changing user1 to Alicia: {id_to_name}")
print(f"ID for Alicia: {id_to_name.get_key('Alicia')}")
print(f"ID for Alice (safe method): {id_to_name.get_key_safe('Alice')}")

# Overwriting a value (which implicitly changes the associated key)
id_to_name['user4'] = 'Charlie'
print(f"After assigning user4 to Charlie: {id_to_name}")
print(f"ID for Charlie: {id_to_name.get_key('Charlie')}")
print(f"Does it contain user3? {id_to_name.__contains__('user3')}")