HW3.7. Demo: Fibonacci function, file upload, external grading

This is a demo of using the Python autograder with an file upload interface. Note that if the student's uploaded filename is different than user_code.py then the correct filename should be set in student_code_file in the PLTestCase class. Here we set it to fib.py to match the file upload.

The Fibonacci numbers are 1, 1, 2, 3, 5, 8, ..., where each number is the sum of the two before it. These are numbered $F_1, F_2, \ldots$, and \[ F_n = F_{n-1} + F_{n-2}. \]

Write a Python function fib that takes a number n and returns the n^th Fibonacci number, $F_n$.

Your code snippet should define the following variables: