Idiomatic programming
I've opined that GIS programmers should be taught to use Python idioms in the classroom. Less code, fewer bugs, efficiency, and to a smaller degree, socialization into the community of Python programmers are what I see as the happy results. I take it as a given that one wants to use and modify the code of others, share code with others, and see it all improve, which is why I value socialization. "Open Source" isn't just about the license, it's also about code as conversation. Because I've been learning Python (and computer programming in general) as I go, I've written as much clunky Python code as anyone else. Regretfully, I've even exposed some learners to clunky code in workshops. Looking back, I'd prefer to have been taught, and to have taught others, idiomatic Python.
I expect that opinions more informed than mine on the subject of language idioms are likely to appear in comments on Tim Bray's post on idiomatic Clojure.