Why does my python not add current working directory to the path?

Whether or not the current directory is in sys.path, import statements usually look like:

import mymodule

The code you wrote looks like:

import 'mymodule.py'

It is the script's directory that is added, not the current directory. If you turn inner_folder/ into a package then you can use python -m inner_folder.myscript in order to run the script while having app/ added to sys.path.