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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 validate(self, guide):
 """ Validate guide object """

        if is_string(guide):
            guide = Registry['guide_{}'.format(guide)]()

        if not isinstance(guide, guide_class):
            raise PlotnineError(
                "Unknown guide: {}".format(guide))
        return guide