PyQt4 | What is the best way to read a list from a file?

Question

PyQt

# Python 3. PyQt4
I want to load the initial data from the file for the test calculation. In the file, the data is written as a list, i.e.:
[20, 8, 4]
There is a code that reads this data from the file and inserts it into the fields:

def on_open_isd (self):
        options = QtGui.QFileDialog.Options()
        self.fileName = QtGui.QFileDialog.getOpenFileName(self, "Открыть как", "ИД. Расчёт объёма.txt",
                                                           "Text Files (*.txt)", options=options)  
                  
        if self.fileName:
            self.readFile = open(self.fileName, 'r', encoding='utf-8')
            open_isd = self.readFile.read()
            self.readFile.close()
        open_isd = open_isd[1:-1].replace(' ','')
        open_isd = open_isd.split(',')  
        self.pole_a.setText(str(open_isd[0]))
        self.pole_b.setText(str(open_isd[1]))
        self.pole_h.setText(str(open_isd[2]))

However, I don't like this approach. I would like to immediately extract the variable from the file in the form of a list, so that I do not have to translate into the python language.
1) Ideally, it would be possible to connect the module through a dialog box, but this method is not familiar to me. As far as I understand it doesn't exist.
2) How can I improve the function given by me in this version.
3) And also if there is more than one list in the file?

Answer 1

import ast
ast.literal_eval("[20, 8, 4]")

If there is more than one list, then it all depends on the record format. Most likely at first it is necessary to parse as the regular text.