How to sort a QTableView?

sorting_qtableview.py

# Applying a sort feature in a QTableView

import sys
from PyQt5.QtCore import (Qt,
                          QModelIndex,
                          QAbstractTableModel,
                          QSortFilterProxyModel)
from PyQt5.QtWidgets import (QApplication,
                             QTableView)

HEADER = ['Qty', 'Fruit']
DATA = [[10, 'Starfruit'],
        [12, 'Orange'],
        [54, 'Kiwi'],
        [7, 'Bapples']]


# Creating the table model
class SortingTableModel(QAbstractTableModel):

    def __init__(self, parent=None):

        super().__init__(parent)

    def headerData(self, section, orientation, role):

        if role == Qt.DisplayRole:
            if orientation == Qt.Horizontal:
                return HEADER[section]

    def data(self, index, role):

        row = index.row()
        col = index.column()

        if role == Qt.DisplayRole:
            value = DATA[row][col]
            return value

    def columnCount(self, parent):

        return len(HEADER)

    def rowCount(self, parent):

        return len(DATA)

    def insertRows(self, position, rows, parent=QModelIndex()):

        self.beginInsertRows(parent, position, position + rows - 1)
        self.endInsertRows()
        return True


if __name__ == '__main__':
    app = QApplication(sys.argv)

    # How to apply sorting in a QTableView

    # Step 1: create the model for the QTableView
    tablemodel = SortingTableModel()
    tablemodel.insertRows(len(DATA), 1)

    # Step 2: create the sorter model
    sortermodel = QSortFilterProxyModel()
    sortermodel.setSourceModel(tablemodel)
    sortermodel.setFilterKeyColumn(3)

    # Step 3: setup the QTableView to enable sorting
    tableview = QTableView()
    tableview.setWindowTitle('Sorting QTableView')
    tableview.setModel(sortermodel)
    tableview.setSortingEnabled(True)
    tableview.sortByColumn(1, Qt.AscendingOrder)   # sorting via 'Fruit' header
    tableview.show()

    sys.exit(app.exec())

difficult for me, but also thank u!

I don´t understand where "data()" and the other methods are called