Trouble opening a file using PyQt5 getOpenFileName

I want the user to open a file, the file name is passed to a function that uses the file for saving some data. I am using PyQt5 getOpenFileName for this:

fileName, _ = QFileDialog.getOpenFileName(None, "Open Data File")

But, I receive this error message: "Process finished with exit code -1073740791 (0xC0000409)". I am using python 3.7.1 and pyqt 5.9.2. My question is how I can fix this error.

Edit: Here is a sample code:

import pandas as pd
import csv
from PyQt5.QtWidgets import QFileDialog
import os
def saveSubjectList(FileNamePath,subjectList):
    columns = list(subjectList[0].__dict__.keys())
    vals = []
    for iSub in range(len(subjectList)):
        valsSub = subjectList[iSub].__dict__.values()
        vals.append(valsSub)

    subject_pd = pd.DataFrame(vals, columns=columns)
    subject_pd.to_csv(FileNamePath)

def loadSubjectList(FileNamePath):
    csvFile = open(FileNamePath, 'r')
    csvFileArray = []
    for row in csv.reader(csvFile):
        csvFileArray.append(row[1:])

    keys = csvFileArray[0]
    subList = []

    for sub in csvFileArray[1:]:
        subject1 = Subject(sub[0])
        for val, key in zip(sub, keys):
            setattr(subject1, key, val)
        subList.append(subject1)
    for item in range(len(subList)):
        print(subList[item].__dict__)

class Subject:
    def __init__(self, Id):
        self.Id = Id
        self.Name = ""
        self.FrameNumberList = []
        self.Color = [0, 1, 0]


if __name__ == '__main__':

    subjectList = []
    for i in range(2):
        subject1 = Subject(i)
        subject1.Name = "Subject" + str(i)
        subject1.FrameNumberList = [i, 10, 23, 23]
        subjectList.append(subject1)
    FileNamePath = os.getcwd()
    fileName = 'New'
    fileNameSuffix = 'csv'
    csvPathAndName = os.path.join(FileNamePath, fileName + '.' + 
     fileNameSuffix)
    saveSubjectList(csvPathAndName, subjectList)
    loadSubjectList(csvPathAndName)

This is the initial code without getOpenFileName, which works fine. Then I removed the lines from FileNamePath= os.getcwd to csvPathAndName=..., and replaced it with:

csvPathAndName, _ = QFileDialog.getOpenFileName(None, "Open Data File")

because I want the user to be able to create or select the file from anywhere in the computer, but then I get the error.