Can’t Step Into Unit Test Code Using PyCharm

I have a unit test file:

unexpected type warning in PyCharm for list.sort lambda

In cleaning up my working code, I’m trying to understand if I should add some sort of type hint.

Why does this two-line Python program give variable output under PyCharm?

Using Windows 7, python.exe 3.8.0 and PyCharm 2019.4.5, I run this program