<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def set(self, key, value):
        "Set value to the key store."
        # if key already in data, update indexes
        if not isinstance(value, dict):
            raise BadValueError(
                'The value {} is incorrect.'
                ' Values should be strings'.format(value))
        _value = deepcopy(value)
        if key in self.data:
            self.delete_from_index(key)
        self.data[key] = _value
        self.update_index(key, _value)