Reimplements the :meth:`QPlainTextEdit.wheelEvent` method.

        :param event: Event.
        :type event: QEvent

def wheelEvent(self, event):
        """
        Reimplements the :meth:`QPlainTextEdit.wheelEvent` method.

        :param event: Event.
        :type event: QEvent
        """

        if event.modifiers() == Qt.ControlModifier:
            if event.delta() == 120:
                self.zoom_in()
            elif event.delta() == -120:
                self.zoom_out()
            event.ignore()
        else:
            QPlainTextEdit.wheelEvent(self, event)