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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_categories(self, app_name):
 """ Returns a list of the categories for an app name. """

        cat_nums = self.apps.get(app_name, {}).get("cats", [])
        cat_names = [self.categories.get("%s" % cat_num, "")
                     for cat_num in cat_nums]

        return cat_names