todo_fileio.py

# pseudocode
# 0 - exit
# 1 - add todo
# 2 - show todo
# 3 - delete todo
# 4 - update todo
import os  # os.system('dos commands')  // cls//pause//notepad area.txt

todos = []  # global variable

def save_todos():
    fo = open('todos.data','w')
    for todo in todos:
        fo.write(f'{todo}\n')
    fo.close()

def load_todos():
    fi = open('todos.data','r')
    for line in fi:
        todos.append(line.strip())
    fi.close()

def add_todo():
    task = input("Enter new task: ")
    todos.append(task)
    print("Added a new task")


def show_todos():
    i = 1
    for todo in todos:
        print(f"{i} - {todo}")
        i = i + 1


def delete_todo():
    show_todos()
    index = input("choose index to delete: ")
    index = int(index) - 1
    del todos[index]
    print("task deleted")


def update_todo():
    show_todos()
    index = input("choose index to delete: ")
    task = input("enter task to update: ")
    index = int(index) - 1
    todos[index] = task
    print("task updated")


ans = -999
load_todos()
while ans != 0:
    os.system("cls")
    print("0 - exit")
    print("1 - add todo")
    print("2 - show todo")
    print("3 - delete todo")
    print("4 - update todo")

    ans = input("Please choose: 0,1,2,3,4: ")
    ans = int(ans)
    os.system("cls")

    if ans == 0:
        print("you choose to exit, good bye!")
        exit(0)

    elif ans == 1:
        print("add todo")
        add_todo()

    elif ans == 2:
        print("show todo")
        show_todos()

    elif ans == 3:
        print("delete todo")
        delete_todo()

    elif ans == 4:
        print("update todo")
        update_todo()

    else:
        print("wrong input, pls try again!")

    save_todos()
    os.system("pause")