It's somewhat apparent just reading through the python that you are self-taught. Some of the idioms used, especially around file handling, are outdated.
For example: you should open files using the with context handler, or at the very least wrap the file open in a try/except block and put file close in the finally block. Garbage collectors will clean up if you don't properly close, but it's better to be explicit.
I would argue that even if the resume passed through to a hiring manager, they would be reticent to hire based off a single code sample in a language listed as a technical skill where there are red flags like this.
Edit: please note that my comments are for Python only, as I'm not proficient in any of the C family languages. Also, as a Biology major who finally broke into dev myself, I'm completely rooting for you!
> Little things like that are going to make people reject you
You make it sound as if his letter is actually being looked at, much less
scrutinized over an MLA nit. No, he will be rejected by a machine long
before that could ever happen.
Little things like that are going to make people reject you, even before they look at your code or resume.