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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 collect_argument(self, step, message):
        '''given a key in the configuration, collect the runtime argument if
           provided. Otherwise, prompt the user for the value.

           Parameters
           ==========
           step: the name of the step, should be 'runtime_arg_<name>'
           message: the content of the step, the message to show the user if the
                    argument <name> is not found under args.

        '''
        if step not in self.data:
            self.data[step] = regexp_prompt(message)