Code Editor Example

The Code Editor example shows how to create a simple editor that has line numbers and that highlights the current line.

Code Editor Screenshot
from PySide6.QtCore import Slot, Qt, QRect, QSize
from PySide6.QtGui import QColor, QPainter, QTextFormat
from PySide6.QtWidgets import QPlainTextEdit, QWidget, QTextEdit


class LineNumberArea(QWidget):
    def __init__(self, editor):
        QWidget.__init__(self, editor)
        self._code_editor = editor

    def sizeHint(self):
        return QSize(self._code_editor.line_number_area_width(), 0)

    def paintEvent(self, event):
        self._code_editor.lineNumberAreaPaintEvent(event)


class CodeEditor(QPlainTextEdit):
    def __init__(self):
        super().__init__()
        self.line_number_area = LineNumberArea(self)

        self.blockCountChanged[int].connect(self.update_line_number_area_width)
        self.updateRequest[QRect, int].connect(self.update_line_number_area)
        self.cursorPositionChanged.connect(self.highlight_current_line)

        self.update_line_number_area_width(0)
        self.highlight_current_line()

    def line_number_area_width(self):
        digits = 1
        max_num = max(1, self.blockCount())
        while max_num >= 10:
            max_num *= 0.1
            digits += 1

        space = 3 + self.fontMetrics().horizontalAdvance('9') * digits
        return space

    def resizeEvent(self, e):
        super().resizeEvent(e)
        cr = self.contentsRect()
        width = self.line_number_area_width()
        rect = QRect(cr.left(), cr.top(), width, cr.height())
        self.line_number_area.setGeometry(rect)

    def lineNumberAreaPaintEvent(self, event):
        painter = QPainter(self.line_number_area)
        painter.fillRect(event.rect(), Qt.lightGray)
        block = self.firstVisibleBlock()
        block_number = block.blockNumber()
        offset = self.contentOffset()
        top = self.blockBoundingGeometry(block).translated(offset).top()
        bottom = top + self.blockBoundingRect(block).height()

        while block.isValid() and top <= event.rect().bottom():
            if block.isVisible() and bottom >= event.rect().top():
                number = str(block_number + 1)
                painter.setPen(Qt.black)
                width = self.line_number_area.width()
                height = self.fontMetrics().height()
                painter.drawText(0, top, width, height, Qt.AlignRight, number)

            block = block.next()
            top = bottom
            bottom = top + self.blockBoundingRect(block).height()
            block_number += 1

    @Slot()
    def update_line_number_area_width(self, newBlockCount):
        self.setViewportMargins(self.line_number_area_width(), 0, 0, 0)

    @Slot()
    def update_line_number_area(self, rect, dy):
        if dy:
            self.line_number_area.scroll(0, dy)
        else:
            width = self.line_number_area.width()
            self.line_number_area.update(0, rect.y(), width, rect.height())

        if rect.contains(self.viewport().rect()):
            self.update_line_number_area_width(0)

    @Slot()
    def highlight_current_line(self):
        extra_selections = []

        if not self.isReadOnly():
            selection = QTextEdit.ExtraSelection()

            line_color = QColor(Qt.yellow).lighter(160)
            selection.format.setBackground(line_color)

            selection.format.setProperty(QTextFormat.FullWidthSelection, True)

            selection.cursor = self.textCursor()
            selection.cursor.clearSelection()

            extra_selections.append(selection)

        self.setExtraSelections(extra_selections)
import sys
from PySide6.QtWidgets import QApplication
from codeeditor import CodeEditor

"""PySide6 port of the widgets/codeeditor example from Qt5"""

if __name__ == "__main__":
    app = QApplication([])
    editor = CodeEditor()
    editor.setWindowTitle("Code Editor Example")
    editor.show()
    sys.exit(app.exec())