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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 import_it(cls):
 """ Performs the import only once. """

        if not cls in cls._FEATURES:
            try:
                cls._FEATURES[cls] = cls._import_it()
            except ImportError:
                raise cls.Error(cls._import_error_message(), cls.Error.UNSATISFIED_IMPORT_REQ)
        return cls._FEATURES[cls]