Python and Qt: Read text file in QTextEdit - program crashes with exit code -1073740791 (0xC0000409)

The following code:

self.texteditor = QTextEdit ('')

def openmenu ():
    filename = QFileDialog.getOpenFileName (self, 'open file', '', 'text files (* .txt)')
    filename = os.path.abspath (filename [0])
    program settings.path openfile = filename
    file content = '' .join (open (file name, encoding = "utf8"). readlines ())
    self.texteditor.setText (file content)

When testing the function I got the following with a text file Error message: Process finished with exit code -1073740791 (0xC0000409)

Question: What can I do against it?

I have recreated what you want with the code you gave and got this to work

import sys
import os

from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtCore import *


class Wnd(QMainWindow):
    def __init__(self, parent=None):
        super().__init__(parent)

        self.initUI()
        self.menuoffnen()
        pass

    def initUI(self):
        self.setGeometry(200, 200, 800, 600)
        self.layout = QVBoxLayout()
        self.layout.setContentsMargins(0, 0, 0, 0)
        self.setLayout(self.layout)

        self.texteditor = QPlainTextEdit('')
        font = QFont()
        font.setPointSize(12)
        self.texteditor.setFont(font)
    
        #self.layout.addWidget(editormenu) # Editormenü
    
        self.setCentralWidget(self.texteditor) # Eingabefeld für Texdateien

        self.setWindowTitle("NodeEditor")
        self.show()

    def menuoffnen(self):
        dateiname = QFileDialog.getOpenFileName(self, 'Datei öffnen','','Textdateien (*.txt)')
        dateiname = os.path.abspath(dateiname[0])
        dateininhalt = ''.join(open(dateiname, encoding="utf-8").readlines())
        self.texteditor.setPlainText(dateininhalt)
        self.setWindowTitle(os.path.basename(dateiname) + " - Marlems PQTTexteditor")

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

    wnd = Wnd()

    sys.exit(app.exec_())

I have tried it with a simple txt file and it worked without errors. Could you test it with your file?

I also find that you forgot to pass self as a parameter into menuoffnen, or is it again a problem in the post?