> I can be 100% sure that: `self` is an object with an attribute rfile, `=` is the assignment operator, there is a method `readline` that get's called with an integer argument 65537.

I think this is overstating things, eg, the class `self` belongs to might have defined __getattribute__, __setattr__, etc, so the things you know for 100% certain about that line of code in isolation don't really tell you anything about what it does (self does not definitely have that attribute, and that might not be assignment, at least); most of that you assume based on common sense, conventions, figuring the code is "normal", etc, the same as in Lisp. And that's ignoring a trivial case like if the previous line was `f('''`, where f may or may or not call eval.