add/remove line numbers

def _updateNumbers(self, linenumers):
        """
        add/remove line numbers
        """
        b = self.blockCount()
        c = b - linenumers
        if c > 0:
            # remove lines numbers
            for _ in range(c):
                # remove last line:
                self.setFocus()
                storeCursorPos = self.textCursor()
                self.moveCursor(
                    QtGui.QTextCursor.End,
                    QtGui.QTextCursor.MoveAnchor)
                self.moveCursor(
                    QtGui.QTextCursor.StartOfLine,
                    QtGui.QTextCursor.MoveAnchor)
                self.moveCursor(
                    QtGui.QTextCursor.End,
                    QtGui.QTextCursor.KeepAnchor)
                self.textCursor().removeSelectedText()
                self.textCursor().deletePreviousChar()
                self.setTextCursor(storeCursorPos)
        elif c < 0:
            # add line numbers
            for i in range(-c):
                self.appendPlainText(str(b + i + 1))