Often while reading code, we encounter scenarios where we want to get an overview of the code.
Sometimes we are interested in
- viewing the functions present in the code.
- viewing all classes defined in the code.
- viewing all methods of a class
- or just viewing the outer loop of a nested loop code
Most editors allow you to “collapse” a block of code to view just its definition
We could achieve the same and more using some simple key strokes in Vi
Few scenarios are mentioned in the video -> 
NOTE : To make these commands work on Python code you need to set the correct foldmethod as
:set foldmethod=indent
The Vi commands mentioned are as follows :
zM: View all definitions in the file ( Toggle all folds )zo: To open one level of foldzR: To open all foldszM: To close all the folds ( Toggle all folds )