I made changes to my code and hit F5 to run it through IDLE. The code
appeared to run without any errors, but when I closed everything out and
ran it again it turned out to be full of errors.

I am able to replicate this problem with my code and have seen others
have the same problem, but its unclear when and what causes the caching
to take place. I created a test file that only contained "print hello".
I ran this, made changes and then ran it again. The changes were
reflected, but after testing my code, it still cached. 

Attached is a simple python file I used to test everything out. Run the
test, then comment out the Struct class and run it again. No errors
should appear, but if you close the code, reopen it and then run it
again it will error.