Why are quotes necessary for opening files?

I was wondering why trying to open a file without putting quotes around it gives back a not defined error. For example opening AppleStore.csv with open(AppleStore.csv) vs open(‘AppleStore.csv’).

A function parameter supports particular data types. The open function is:

open(file, ...)

The file parameter accept the path to the document you want to open as a string or byte.

When you put anything inside a single, double or triple quotation mark in Python, it is a string.