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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 close(self):
 """Closes the connection. No further operations are allowed, either on the connection or any of its cursors, once the connection is closed. If the connection is used in a ``with`` statement, this method will be automatically called at the end of the ``with`` block. """

        if self._closed:
            raise ProgrammingError('the connection is already closed')
        for cursor_ref in self._cursors:
            cursor = cursor_ref()
            if cursor is not None and not cursor._closed:
                cursor.close()
        self._client.close_connection(self._id)
        self._client.close()
        self._closed = True