Before using the sys module I ran this code like this python hangman.py.When you run the code after the using the sys module you will see ['hangman.py'].As you see sys.argv command gives a list.First item of this list is name of the our project file name.
I ran the same program as follows ['hangman.py,'cpsc231-lexic.txt']. I added second element to the list which is txt.file name.Then I assigned the filename to the 2nd element of sys.argv in the code,as a result the filename we called was 'cpsc231-lexic.txt'.
You can't run this code like python hangman.py anymore.You must write ==> python hangman.py cpsc231-lexic.txt if you don't write you will give an error message.
HAVE FUN!