Pyside2-Linenumbers在人错误的时候改变了字体的家庭/尺寸

我看着这个代码编辑例从官方Qt5网站 https://doc.qt.io/qt-5/qtwidgets-widgets-codeeditor-example.html. 它是用C++编写的但我实现它在Python使用Pyside2.

例代码的工作，但是，当我试图改变的字体的家庭和大小 QPlainTextEdit 事情开始变得混乱。 我试着调整一个很大的不同领域的使用 fontMetrics 确定的高度，等等。

这里是一个小例的重现的问题

import sys
import signal
from PySide2.QtCore import Qt, QSize, QRect
from PySide2.QtGui import QPaintEvent, QPainter, QColor, QResizeEvent
from PySide2.QtWidgets import QWidget, QPlainTextEdit, QVBoxLayout
from PySide2 import QtCore
from PySide2.QtWidgets import QApplication


FONT_SIZE = 20
FONT_FAMILY = 'Source Code Pro'


class PlainTextEdit(QPlainTextEdit):
    def __init__(self, parent=None):
        super().__init__(parent)

        self.init_settings_font()

    def init_settings_font(self):
        font = self.document().defaultFont()

        font.setFamily(FONT_FAMILY)
        font.setFixedPitch(True)
        font.setPixelSize(FONT_SIZE)
        self.document().setDefaultFont(font)


class LineNumberArea(QWidget):
    TMP = dict()

    def __init__(self, editor):
        super().__init__(editor)
        self._editor = editor

        self._editor.blockCountChanged.connect(lambda new_count: self._update_margin())
        self._editor.updateRequest.connect(lambda rect, dy: self._update_request(rect, dy))

        self._update_margin()

    def width(self) -> int:
        # we use 1000 as a default size, so from 0-9999 this length will be applied
        _max = max(1000, self._editor.blockCount())
        digits = len(f'{_max}')
        space = self._editor.fontMetrics().horizontalAdvance('0', -1) * (digits + 1) + 6
        return QSize(space, 0).width()

    def _update_line_geometry(self):
        content_rect = self._editor.contentsRect()
        self._update_geometry(content_rect)

    def _update_geometry(self, content_rect: QRect):
        self.setGeometry(
            QRect(content_rect.left(), content_rect.top(), self.width(), content_rect.height())
        )

    def _update_margin(self):
        self._editor.setViewportMargins(self.width(), 0, 0, 0)

    def _update_request(self, rect: QRect, dy: int):
        self._update(0, rect.y(), self.width(), rect.height(), self._editor.contentsRect())

        if rect.contains(self._editor.viewport().rect()):
            self._update_margin()

    def _update(self, x: int, y: int, w: int, h: int, content_rect: QRect):
        self.update(x, y, w, h)
        self._update_geometry(content_rect)

    # override
    def resizeEvent(self, event: QResizeEvent) -> None:
        self._update_line_geometry()

    # override
    def paintEvent(self, event: QPaintEvent):
        painter = QPainter(self)
        area_color = QColor('darkgrey')

        # Clearing rect to update
        painter.fillRect(event.rect(), area_color)

        visible_block_num = self._editor.firstVisibleBlock().blockNumber()
        block = self._editor.document().findBlockByNumber(visible_block_num)
        top = self._editor.blockBoundingGeometry(block).translated(self._editor.contentOffset()).top()
        bottom = top + self._editor.blockBoundingRect(block).height()
        active_line_number = self._editor.textCursor().block().blockNumber() + 1

        # font_size = storage.get_setting(Constants.Editor_font_size).value
        font = self._editor.font()

        while block.isValid() and top <= event.rect().bottom():
            if block.isVisible() and bottom >= event.rect().top():
                number_to_draw = visible_block_num + 1

                if number_to_draw == active_line_number:
                    painter.setPen(QColor('black'))
                else:
                    painter.setPen(QColor('white'))

                font.setPixelSize(self._editor.document().defaultFont().pixelSize())
                painter.setFont(font)

                painter.drawText(
                    -5,
                    top,
                    self.width(),
                    self._editor.fontMetrics().height(),
                    int(Qt.AlignRight | Qt.AlignHCenter),
                    str(number_to_draw)
                )

            block = block.next()
            top = bottom
            bottom = top + self._editor.blockBoundingGeometry(block).height()
            visible_block_num += 1

        painter.end()

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

    signal.signal(signal.SIGINT, signal.SIG_DFL)

    window = QWidget()
    layout = QVBoxLayout()
    editor = PlainTextEdit()
    line_num = LineNumberArea(editor)

    layout.addWidget(editor)
    window.setLayout(layout)

    window.show()

    sys.exit(app.exec_())

最大的一个问题是，似乎是一个顶部保证金抵消在退出明文我无法动态得到的"行号"的部件。 并设定时的编辑字体的画家的数字都不会画出同样的尺寸!?

没有人知道如何调整符号相同水平的相应文本，也得到他们是相同的大小在一个动态的方式，意思是如果字体将是定于别的东西他们都应该自动调整。