Highlighting Multiple lines on QTextEdit document

Question

Attempting to create a way (using PyQt5 and Python 3) to highlight a multiple line number in the document of the QTextEdit widget. Here is the attempted code below (with many thanks to those in stackoverflow who answered similar questions before):

from PyQt5.QtCore import Qt, QTimer, QEventLoop
from PyQt5.QtGui import QTextBlockFormat, QTextBlock, QTextCursor
from PyQt5.QtWidgets import QWidget, QApplication, QTextEdit, QVBoxLayout

sample = """
Test document...
This is Line 2
This is Line 3
Explanation:
  This is an explanation section. Here we explain.
  Explanation section ends.
Back to body of document.
This is Line 8.
This is the last line.
"""


class Window(QWidget):
    def __init__(self):
        super(Window, self).__init__()
        self.editor = QTextEdit(self)
        self.editor.setText(sample)

        self.format_normal = QTextBlockFormat()
        self.format_normal.setBackground(Qt.white)

        self.highlight_format = QTextBlockFormat()
        self.highlight_format.setBackground(Qt.yellow)

        self.cursor = self.editor.textCursor()

        layout = QVBoxLayout(self)
        layout.addWidget(self.editor)

    def setLineFormat(self, lineNumber, format):
        """ Sets the highlighting of a given line number in the QTextEdit"""
        #self.cursor.clearSelection()
        self.cursor.select(QTextCursor.Document)
        self.cursor.setBlockFormat(self.format_normal)

        self.cursor = QTextCursor(self.editor.document().findBlockByNumber(lineNumber))
        self.cursor.setBlockFormat(format)

    def cycle_through_lines(self):
        """ Cycles through specified lines. """
        line_nu[5,10,15,20]
        for ii in line_num:
            self.setLineFormat(ii, self.highlight_format)
            self.pause(1000)

    def pause(self, duration):
        """ Provides a pause of a specified duration. """
        loop = QEventLoop()
        QTimer.singleShot(duration, loop.quit)
        loop.exec_()


if __name__ == '__main__':

    import sys
    app = QApplication(sys.argv)
    window = Window()
    window.setGeometry(500, 150, 300, 300)
    window.show()
    window.cycle_through_lines()
    sys.exit(app.exec_())

Here the problem is a able to hilite only last no in the list.