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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 previous(self):
 """Return the previous page. The page label is defined in ``settings.PREVIOUS_LABEL``. Return an empty string if current page is the first. """

        if self._page.has_previous():
            return self._endless_page(
                self._page.previous_page_number(),
                label=settings.PREVIOUS_LABEL)
        return ''