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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 schema(self):
 """ Returns the database schema as a string. """

        c = self.conn.cursor()
        c.execute(
            '''
            SELECT sql FROM sqlite_master
            ''')
        results = []
        for i, in c:
            if i is not None:
                results.append(i)
        return '\n'.join(results)