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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 get_template_names(self):
 """ Return the page's specified template name, or a fallback if one hasn't been chosen. """

        posted_name = self.request.POST.get('template_name')
        if posted_name:
            return [posted_name,]
        else:
            return super(PagePreviewView, self).get_template_names()