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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def eval(self, command):
 """ Evaluate the given string against all registered commands and return the defined response. :type command: str :param command: The command that is evaluated. :rtype: str or None :return: The response, if one was defined. """

        for cmd, response in self.response_list:
            if not cmd.match(command):
                continue
            if response is None:
                return None
            elif hasattr(response, '__call__'):
                return response(command)
            else:
                return response
        if self.strict:
            raise Exception('Undefined command: ' + repr(command))
        return None