stop = False
marks = {}

while not stop:
    print("1 … Load marks from file")
    print("2 … Save marks to file")
    print("3 … Add/Update a subject with mark")
    print("4 … Show all marks")
    print("0 … exit")

    command = input("Enter your choice:")
    if(not command.isnumeric()):
        print ("Please enter a number!")
        continue

    command = int(command)

    if(not (command <= 4 and command >= 0)):
        print("Please choose one of the choices given!")
        continue


    if command == 0:
        print("Exiting...")
        stop = True

    if command == 1:
        file_name = input("Enter filename: ")
        try:
            with open(file_name) as f:
                for line in f:
                    subject, mark = line.split(';')
                    mark = mark.replace('\n', '')
                    sub_marks = []

                    for i in range(0, len(mark),1):
                        sub_marks.append(int(mark[i]))

                    marks[subject] = sub_marks

        except FileNotFoundError:
            print('File not found!')
        except IOError:
            print('Error reading file!')
        else:
            print('Reading finished')

    elif command == 2:
        file_name = input("Enter filename: ")
        try:
            with open(file_name, 'w') as f:
                for subject, mark in marks.items():
                    f.write(subject + ";" + ''.join(map(str, mark)) + '\n')
        except IOError:
            print('Error writing file!')
        else:
            print("Saved!")

    elif command == 3:
        subject = input("Subject:")
        mark = input("Mark:\t")
        try:
            if subject in marks:
                marks[subject].append(int(mark))
            else:
                marks[subject] = [int(mark)]
        except ValueError:
            print("Mark has to be a number!")

    elif command == 4:
        for item, value in marks.items():
            print(item + "\t->\t" + str(value))