Покурочте код питон пайкюти 5

import sys

from PyQt5.QtWidgets import QApplication, QMainWindow
from qt import Ui_MainWindow


class Main(QMainWindow, Ui_MainWindow):
def __init__(self):
super().__init__()
self.setupUi(self)
self.setup()

def setup(self):
self.pushButton.clicked.connect( self.open _file)
self.pushButton_2.clicked.connect(self.save_file)
self.pushButton_3.clicked.connect(self.create_file)

def open_file(self):
file = self.lineEdit.text()
try:
with open(file) as f:
self.plainTextEdit.setPlainText( f.read ())
self.label.setText('Редактор файлов')
except Exception:
self.label.setText('Такой файл не найден')

def save_file(self):
file = self.lineEdit.text()
try:
open(file)
with open(file, 'w') as f:
f.write(self.plainTextEdit.toPlainText())
except Exception:
self.label.setText('Такой файл не найден')

def create_file(self):
file = self.lineEdit.text()
with open(file, 'w') as f:
f.write(self.plainTextEdit.toPlainText())
self.label.setText('Редактор файлов')


if __name__ == '__main__':
app = QApplication(sys.argv)
ex = Main()
ex.show()
sys.exit(app.exec())
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