How to change the font of a specific tab in QTabWidget in Pyside2?

Question

After an event is triggered, I want to change the font of a specific tab to use a bold font, rather than non-bold.

qtabwidget.tabs[4].setFontWeight(Bold)

How to do this?

Answer 1

One possible solution is to use a QProxyStyle:

import sys

from PySide2 import QtCore, QtGui, QtWidgets


class TabBarStyle(QtWidgets.QProxyStyle):
    def drawControl(self, element, option, painter, widget=None):
        index = -1
        if element == QtWidgets.QStyle.CE_TabBarTab:
            if isinstance(widget, TabBar):
                for i in widget.fonts.keys():
                    if widget.tabRect(i) == option.rect:
                        index = i
                        break
            if index > -1:
                painter.save()
                painter.setFont(widget.fonts[index])
        super(TabBarStyle, self).drawControl(element, option, painter, widget)
        if index > -1:
            painter.restore()


class TabBar(QtWidgets.QTabBar):
    def __init__(self, parent=None):
        super(TabBar, self).__init__(parent)
        self._fonts = dict()

    @property
    def fonts(self):
        return self._fonts


class MainWindow(QtWidgets.QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)

        self.tab_widget = QtWidgets.QTabWidget()
        self.setCentralWidget(self.tab_widget)

        self.tab_bar = TabBar()
        self.tabbar_style = TabBarStyle(self.tab_bar.style())
        self.tab_bar.setStyle(self.tabbar_style)
        self.tab_widget.setTabBar(self.tab_bar)

        self.tab_widget.addTab(QtWidgets.QWidget(), "Foo")
        self.tab_widget.addTab(QtWidgets.QWidget(), "Bar")
        self.tab_widget.addTab(QtWidgets.QWidget(), "Baz")

        font = self.tab_widget.font()
        font.setBold(True)
        self.tab_bar.fonts[1] = font
        self.tab_bar.update()


def main():
    app = QtWidgets.QApplication(sys.argv)
    app.setStyle("fusion")
    w = MainWindow()
    w.show()
    sys.exit(app.exec_())


if __name__ == "__main__":
    main()