为什么在使用 setCharFormat() 时会出现堆栈溢出错误？

Question

我正在编写一个方法，show_spelling_errors()，它遍历保存在列表 self.tokens 中的自定义对象，并使用每个对象的属性来更改 Qt TextEdit 小部件中某些字体的颜色。 show_spelling_errors() 由另一个方法调用，该方法连接到 Qt 中的 textChanged 信号，因此它会在用户输入小部件的任何时候运行。方法定义如下：

def show_spelling_errors(self):
    try:
        cursor = self.textEdit.textCursor()
        incorrect_format = cursor.charFormat()
        incorrect_format.setForeground(QtCore.Qt.GlobalColor.red)
        for token in self.tokens:
            if not token.is_spelled_correctly:
                print("is spelled correctly: " + str(token.is_spelled_correctly))
                cursor.movePosition(cursor.MoveOperation.Start, cursor.MoveMode.MoveAnchor)
                cursor.movePosition(cursor.MoveOperation.NextWord, cursor.MoveMode.MoveAnchor, token.word_index)
                cursor.movePosition(cursor.MoveOperation.EndOfWord, cursor.MoveMode.KeepAnchor)
                print("selection start " + str(cursor.selectionStart()))
                print("selection end  " + str(cursor.selectionEnd()))
                # cursor.setCharFormat(incorrect_format)
                cursor.clearSelection()

如果我完全按照上面的方式运行代码，一切都会按预期运行。但是，如果我取消注释倒数第二行（实际上应该更改字体颜色），则循环不再终止，而是在 self.tokens 的第一个成员上无休止地循环，然后最终导致堆栈溢出。我很困惑，在循环中包含这条语句会导致循环的行为（我认为应该是无关的？）以这种方式改变。

编辑：下面是重现此行为所需的代码

from PyQt6.QtWidgets import QApplication, QWidget, QTextEdit, QVBoxLayout
from PyQt6 import QtCore
import sys
import re
import traceback
from spellchecker import SpellChecker


class Token:
    def __init__(self, chars, spell, start=0, word_index=0):
        self.word_index = word_index
        self.content = chars
        self.token_length = len(chars)
        self.start_pos = start
        self.end_pos = start + self.token_length
        self.is_spelled_correctly = len(spell.unknown([chars])) < 1

class TextEditDemo(QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)

        self.setWindowTitle("QTextEdit")
        self.resize(300, 270)
        self.spell = SpellChecker()
        self.textEdit = QTextEdit()

        layout = QVBoxLayout()
        layout.addWidget(self.textEdit)
        self.setLayout(layout)

        self.tokens = None
        self.textEdit.textChanged.connect(self.handle_text)

    def handle_text(self):
        self.tokenize_text()
        self.show_spelling_errors()

    def show_spelling_errors(self):
        try:
            cursor = self.textEdit.textCursor()
            incorrect_format = cursor.charFormat()
            incorrect_format.setForeground(QtCore.Qt.GlobalColor.red)
            for token in self.tokens:
                if not token.is_spelled_correctly:
                    print("is spelled correctly: " + str(token.is_spelled_correctly))
                    cursor.movePosition(cursor.MoveOperation.Start, cursor.MoveMode.MoveAnchor)
                    cursor.movePosition(cursor.MoveOperation.NextWord, cursor.MoveMode.MoveAnchor, token.word_index)
                    cursor.movePosition(cursor.MoveOperation.EndOfWord, cursor.MoveMode.KeepAnchor)
                    print("selection start " + str(cursor.selectionStart()))
                    print("selection end  " + str(cursor.selectionEnd()))
                    cursor.setCharFormat(incorrect_format)
                    cursor.clearSelection()

        except:
            traceback.print_exc()

    def tokenize_text(self):
        try:
            print("tokenizing...")
            text = self.textEdit.toPlainText()
            text_seps = re.findall(' .', text)
            current_pos = 0
            start_positions = [current_pos]
            for sep in text_seps:
                current_pos = text.find(sep, current_pos) + 1
                start_positions.append(current_pos)

            self.tokens = [
                Token(string, self.spell, start, word_ind) for
                word_ind, (start, string) in
                enumerate(zip(start_positions, text.split()))
            ]
        except:
            traceback.print_exc()

app = QApplication([])
win = TextEditDemo()
win.show()
sys.exit(app.exec())

Answer 1

解释：

如果您查看文档以获取 QTextEdit 的 textChanged 信号：

void QTextEdit::textChanged() 每当 文件内容变更；例如，当插入文本或 删除，或应用格式时。

注意：属性 html 的通知信号。属性的通知信号 降价。

_{（强调我的）}

这表示在改变格式时也会触发，所以产生了无限循环。

解决办法：

一种可能的解决方案是使用 blockSignals 来阻止信号：

def handle_text(self):
    self.textEdit.blockSignals(True)
    self.tokenize_text()
    self.show_spelling_errors()
    self.textEdit.blockSignals(False)

但更优雅的解决方案是使用QSyntaxHighlighter：

import re
import sys
from functools import cached_property

from PyQt6.QtCore import Qt
from PyQt6.QtGui import QSyntaxHighlighter, QTextCharFormat
from PyQt6.QtWidgets import QApplication, QWidget, QTextEdit, QVBoxLayout

from spellchecker import SpellChecker


class SpellSyntaxHighlighter(QSyntaxHighlighter):
    WORD_REGEX = re.compile(
        r"\b[^\d\W]+\b"
    )  # https://stackoverflow.com/a/29375664/6622587

    @cached_property
    def text_format(self):
        fmt = QTextCharFormat()
        fmt.setUnderlineColor(Qt.GlobalColor.red)
        fmt.setUnderlineStyle(QTextCharFormat.UnderlineStyle.SpellCheckUnderline)
        return fmt

    @cached_property
    def spellchecker(self):
        return SpellChecker()

    def highlightBlock(self, text):
        misspelled_words = set()
        for match in self.WORD_REGEX.finditer(text):
            word = text[match.start() : match.end()]
            if len(word) > 1 and self.spellchecker.unknown([word]):
                misspelled_words.add(word)
        for misspelled_word in misspelled_words:
            for m in re.finditer(fr"\b{misspelled_word}\b", text):
                self.setFormat(m.start(), m.end() - m.start(), self.text_format)


class TextEditDemo(QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)

        self.setWindowTitle("QTextEdit")
        self.resize(300, 270)
        self.textEdit = QTextEdit()

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

        self.highlighter = SpellSyntaxHighlighter(self.textEdit.document())


def main():

    app = QApplication([])
    win = TextEditDemo()
    win.show()
    sys.exit(app.exec())


if __name__ == "__main__":
    main()