Python3 using basic loops to achieve multilevel catalogs (ideas)

First, multilevel directory design:

1. Display menus and access menus in a circular manner

2. Set the flag bit to provide a fallback to the previous level menu

2. Set the flag bit to provide an exit procedure

Second, Attention points:

1. Menu style, hierarchical relationship don't mess up.

2. When an error is entered, keep it under the current view

3. Notice whether the flag bit has an effect on other loops after use, or you need to go to another branch

　　

Python3 using basic loops to achieve multilevel catalogs (ideas)