Add import sys to file.py

Summary

A conditional sys.exit(1) was added to file.py in a recent MR, but import sys was not added to the top of the file. This was an oversight and will cause problems.

Steps to reproduce

1. Open file.py
2. Ctrl + F "sys"

Context

There is only one system call in the file and it only is used if file is about to pass a non zero return code. As such, the error only comes up when when something has already gone wrong. That is why the error was not caught in testing.

Acceptance criteria

import sys is at the top of the file with the other import commands.