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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 set_arg(self, value):
 """ Set the query param in self.args based on the prefix and arg index and auto increment the arg_index :return: the string placeholder for the arg :rtype: str """

        named_arg = '{0}A{1}'.format(self.arg_prefix, self.arg_index)
        self.args[named_arg] = value
        self.arg_index += 1
        return named_arg