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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 sorted_migrations(self):
 """ Sort migrations if necessary and store in self._sorted_migrations """

        if not self._sorted_migrations:
            self._sorted_migrations = sorted(
                self.migration_registry.items(),
                # sort on the key... the migration number
                key=lambda migration_tuple: migration_tuple[0])

        return self._sorted_migrations