如何确保python dict键是小写的？

class LowercaseDict(dict):
    def __setitem__(self, key, value):
        super().__setitem__(key.lower(), value)

    def __getitem__(self, key):
        return super().__getitem__(key.lower())

    def __contains__(self, key):
        return super().__contains__(key.lower())

    def get(self, key, default=None):
        return super().get(key.lower(), default)

    def update(self, other=None, **kwargs):
        if other is not None:
            for key, value in other.items():
                self[key] = value
        for key, value in kwargs.items():
            self[key] = value

# 使用示例
d = LowercaseDict()
d['Key1'] = 'Value1'
d['KEY2'] = 'Value2'
d['key3'] = 'Value3'

print(d)  # 输出: {'key1': 'Value1', 'key2': 'Value2', 'key3': 'Value3'}
print(d['KEY1'])  # 输出: 'Value1'