Override Qt method

        Select line, and starts selection

def mousePressEvent(self, event):
        """Override Qt method

        Select line, and starts selection
        """
        line_number = self.editor.get_linenumber_from_mouse_event(event)
        self._pressed = line_number
        self._released = line_number
        self.editor.select_lines(self._pressed,
                                 self._released)