Возможно, вы можете использовать QTabWidget::setCornerWidget
...
import sys
from PyQt5 import QtCore, QtWidgets, QtGui
from PyQt5.QtCore import Qt
class Widget(QtWidgets.QTabWidget):
def __init__(self, parent=None):
QtWidgets.QTabWidget.__init__(self, parent)
self.setCornerWidget(QtWidgets.QLabel("Corner Widget"))
self.addTab(QtWidgets.QLabel("Tab 1"), "Tab 1")
self.addTab(QtWidgets.QLabel("Tab 2"), "Tab 2")
self.addTab(QtWidgets.QLabel("Tab ..."), "Tab ...")
if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
w = Widget()
w.show()
app.exec_()