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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 _string_to_substitute(self, mo, methods_dict):
 """ Return the string to be substituted for the match. """

        matched_text, f_name = mo.groups()
        # matched_text is the complete match string. e.g. plural_noun(cat)
        # f_name is the function name. e.g. plural_noun

        # Return matched_text if function name is not in methods_dict
        if f_name not in methods_dict:
            return matched_text

        # Parse the matched text
        a_tree = ast.parse(matched_text)

        # get the args and kwargs from ast objects
        args_list = [self._get_value_from_ast(a) for a in a_tree.body[0].value.args]
        kwargs_list = {
            kw.arg: self._get_value_from_ast(kw.value)
            for kw in a_tree.body[0].value.keywords
        }

        # Call the corresponding function
        return methods_dict[f_name](*args_list, **kwargs_list)