Highlighting specific line in a text editor | PyQt5 Tutorial

In this PyQt5 tutorial, we are going to look how to implement a feature to highlight specific line in a editor giving the line number.

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Source Code:

import sys
from PyQt5.QtWidgets import QApplication, QWidget, QLineEdit, QPlainTextEdit, QVBoxLayout
from PyQt5.QtCore import QRegExp
from PyQt5.QtGui import QColor, QRegExpValidator, QSyntaxHighlighter, QTextCharFormat

class SyntaxHighlighter(QSyntaxHighlighter):
    def __init__(self, parnet):
        super().__init__(parnet)
        self._highlight_lines = {}

    def highlight_line(self, line_num, fmt):
        if isinstance(line_num, int) and line_num >= 0 and isinstance(fmt, QTextCharFormat):
            self._highlight_lines[line_num] = fmt
            block = self.document().findBlockByLineNumber(line_num)
            self.rehighlightBlock(block)

    def clear_highlight(self):
        self._highlight_lines = {}
        self.rehighlight()

    def highlightBlock(self, text):
        blockNumber = self.currentBlock().blockNumber()
        fmt = self._highlight_lines.get(blockNumber)
        if fmt is not None:
            self.setFormat(0, len(text), fmt)

class AppDemo(QWidget):
    def __init__(self):
        super().__init__()
        self.resize(1200, 800)

        mainLayout = QVBoxLayout()

        validator = QRegExpValidator(QRegExp(r'[0-9 ]+'))

        self.lineEdit = QLineEdit()
        self.lineEdit.setStyleSheet('font-size: 30px; height: 50px;')
        self.lineEdit.setValidator(validator)
        self.lineEdit.textChanged.connect(self.onTextChanged)
        mainLayout.addWidget(self.lineEdit)

        self.textEditor = QPlainTextEdit()
        self.textEditor.setStyleSheet('font-size: 30px; color: green')
        mainLayout.addWidget(self.textEditor)

        for i in range(1, 21):
            self.textEditor.appendPlainText('Line {0}'.format(i))

        self.highlighter = SyntaxHighlighter(self.textEditor.document())
        self.setLayout(mainLayout)

    def onTextChanged(self, text):
        fmt = QTextCharFormat()
        fmt.setBackground(QColor('yellow'))

        self.highlighter.clear_highlight()

        try:
            lineNumber = int(text) - 1
            self.highlighter.highlight_line(lineNumber, fmt)
        except ValueError:
            pass

app = QApplication(sys.argv)        
demo = AppDemo()
demo.show()
sys.exit(app.exec_())