import argv

[radix018]

You must be passing less than 4 arguments. The error says, 4 variables are expected but only 3 were given by you.
py ex13.py first 2nd 3rd, this is how it should work.
"ex13.py" = 1st variable (script)
"first" = 2nd variable (first)
"2nd" = 3rd variable (second)
"3rd" = 4th variable (third)

AND WYSS sections refers to "What You Should See" section, which is just below the code.