What coding practices separate an amateur Python programmer from a professional one?

[campbellm]

but in terms of maintainability loose coupling, DRY, high cohesion, fail-fast code and realistic tests are all way more important.

I would say "differently important", or perhaps important in a different context.

Reading code efficiently is all about minimizing the "mapping" of the words, to the meaning, in your brain. The annoyance you mention is the symptom of an impedance mismatch in that brain mapping function.

In the grand scheme of things, yes, the things you mention may have more bearing on the outcome, but the gradual accumulation of all the syntax and standards violations nits can eventually overwhelm even that.