def crypt(rudict, endict) :
    en=""
    s1 = list(texttocrypt.text())
    for i in range(len(s1)):
        for j in range(len(rudict)):
            if s1[i] in rudict :
               error = 0

            else:
                error = 1
    if error == 1:
        QMessageBox.warning(self, "Ошибка", "Обнаружены недопустимые символы")
    else:
        str(texttocrypt.text())

        for i in range(len(s1)):
            index = rudict.index(s1[i])
            en = en + endict[index]
        cryptedtext.setReadOnly(False)
        cryptedtext.setText("")
        print(en)
        cryptedtext.setText(0,en)
        cryptedtext.setReadOnly(True)
self.btn1.clicked.connect(crypt)