In this video, we will talk about the following topics regarding functions in Python.
1- The concept of function
2- what is the Return in functions?
3- How to use one Function in another Function?
4- What are the arbitrary args and arbitrary kwargs?
5- Comment syntax in the function
6- Second mini project

The mini-project is about creating a to-do list. Here is the complete question.

Build a to-do list application using functional programming concepts and the knowledge gained from the previous 10 questions. The application should provide the following features:

1- Add a task to the to-do list.
2- Remove a task from the to-do list.
3- View all tasks in the to-do list.
4- Mark a task as completed.
5- Filter and display only the completed tasks.
6- Calculate and display the count of completed tasks.
7- Calculate and display the average length of task descriptions.

Utilize the functions from the previous 10 questions and adapt them to fit the requirements of the to-do list application. Implement the necessary functions using functional programming concepts such as mapping, filtering, and lambda functions.

Create a runner script that interacts with the application by presenting a menu-based interface to the user. The runner script should allow users to choose from different actions to perform on the to-do list.