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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 select_radio_button(self, key):
 """Helper to select a radio button with key. :param key: The key of the radio button. :type key: str """

        key_index = list(self._parameter.options.keys()).index(key)
        radio_button = self.input_button_group.button(key_index)
        radio_button.click()