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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 _boxFromData(self, messageData):
 """ A box. @param messageData: a serialized AMP box representing either a message or an error. @type messageData: L{str} @raise MalformedMessage: if the C{messageData} parameter does not parse to exactly one AMP box. """

        inputBoxes = parseString(messageData)
        if not len(inputBoxes) == 1:
            raise MalformedMessage()
        [inputBox] = inputBoxes
        return inputBox