web.py

import streamlit as sl
import functions


todos=functions.get_todos()

def add_todo():
    todo=sl.session_state["new_todo"] + "\n"
    todos.append(todo)
    functions.write_todos(todos)
    sl.session_state["new_todo"]=""

sl.title("My Todo App")
sl.subheader("This is my todo app.")
sl.write("This app is to improve productivity")

for index, todo in enumerate(todos):
    checkbox = sl.checkbox(todo, key=todo)
    if checkbox:
        todos.pop(index)
        functions.write_todos(todos)
        del sl.session_state[todo]
        sl.experimental_rerun()

sl.text_input(label="", placeholder="Add a todo...",
              on_change=add_todo, key="new_todo")