The minimal example code below renders the following GUI:

What I would like to achieve, instead, is this (manually edited image):

… which is to say, I would like the column (horizontal) headings to have two lines of text, centered: the top line of text in bigger font size, and the bottom one in smaller font size and bold font.

I originally hoped that I could just use HTML and QCSS styling for this, but

• https://forum.qt.io/topic/30598/solved-how-to-display-subscript-text-in-header-of-qtableview

this is not supported by Qt, you would need to implement a QStyledItemDelegate and set it to your QHeaderView.

The example below shows clearly HTML is not accepted in headings, too.

Unfortunately, I could not find any example that demonstrates how to use a QStyledItemDelegate with an effect similar to what I’m looking for, so I tried something in my code below from some examples I could find – and as the first screenshot shows, obviously it does not work.

So, how can I get a heading that has two lines of text, one under the other, where the second line of text has a different font from the first one?

Code example:

# base of example from https://www.pythonguis.com/tutorials/qtableview-modelviews-numpy-pandas/
import sys
from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.QtCore import Qt, QTimer
from PyQt5.QtWidgets import QStyledItemDelegate, QWidget, QVBoxLayout, QLabel

coltxts = {
  0: "STANDARD_COLUMN_DESCRIPTION",
  1: "ADVANCED_COLUMN_DESCRIPTION",
  2: "VERBOSE_COLUMN_DESCRIPTION",
}

class TableModel(QtCore.QAbstractTableModel):
  def __init__(self, data):
    super(TableModel, self).__init__()
    self._data = data

  def data(self, index, role):
    if role == Qt.DisplayRole:
      return self._data[index.row()][index.column()]

  def headerData(self, section, orientation, role=Qt.DisplayRole): # SO:64287713
    if orientation == Qt.Horizontal:
      if role == Qt.DisplayRole:
        retstr = "Column {}".format(section)
        if section == 0:
          retstr += "<br>{}".format(coltxts[section])
        else:
          retstr += "n{}".format(coltxts[section])
        return retstr
    return super().headerData(section, orientation, role)

  def rowCount(self, index):
    return len(self._data)

  def columnCount(self, index):
    return len(self._data[0])


class MainWindow(QtWidgets.QMainWindow):
  def __init__(self):
    super().__init__()

    self.table = QtWidgets.QTableView()

    data = [
      [4, 9, 2],
      [1, 0, 0],
      [3, 5, 0],
      [3, 3, 2],
      [7, 8, 9],
    ]

    self.model = TableModel(data)
    self.table.setModel(self.model)

    htest_item = TwoLineTableWidgetItemDelegate(self.table)
    self.table.setItemDelegateForColumn(0, htest_item)

    #self.table.horizontalHeader().setStyleSheet("QHeaderView { font-size: 8pt; font-weight: bold; }");

    QTimer.singleShot(10, self.table.resizeColumnsToContents)
    self.setCentralWidget(self.table)


class TwoLineTableWidgetItemDelegate(QStyledItemDelegate): # via SO:52545316, bit of SO:24024815
  """
  Tried to start this by building on:
  /q/52545316/
  /q/24024815/
  """
  def __init__(self, icons, parent=None):
    super(TwoLineTableWidgetItemDelegate, self).__init__(parent)
    self.main_widget = QWidget()
    self.layout = QVBoxLayout()
    self.label_top = QLabel()
    self.label_bottom = QLabel()
    self.layout.addWidget(self.label_top)
    self.layout.addWidget(self.label_bottom)
    self.main_widget.setLayout(self.layout)
  def paint(self, painter, option, index):
    #icon = self.get_icon(index)
    self.label_top.setText(str(index.row()))
    self.label_bottom.setText(str(index.column()))
    #self.main_widget.paint(painter, option.rect, QtCore.Qt.AlignCenter) # no paint here
    self.main_widget.update()


app=QtWidgets.QApplication(sys.argv)
window=MainWindow()
window.show()
app.exec_()