You ask them a whiteboard coding question -- something about manipulating strings or implementing simple searching. Let's ignore the debate of whether this is a productive technique for interviews for now. You ask for Python in this question since you've already covered JavaScript.
The candidate can't remember what the "str" type is called, or how to find substrings in a string, or the difference between "==" and "is" for objects. They ask you to remind them if "join" is a method on sequences or on strings. They write "length()" when they mean "len()".
We've discussed at length on HN the challenges of whiteboard coding. "Nobody's favorite IDE is their conference room whiteboard".
But I feel that, even through the flawed medium of the whiteboard, I'm seeing symptoms of the candidate not really "knowing" Python to the degree I would expect of someone who applied for a job writing it.
None of the people I work with who write Python would ever forget one of these basics. I think they recognize that the ultimate "efficiency" isn't a cheat sheet on your wall, but rather learning and internalizing these tools by repeatedly using them.
Forgive me for setting up what I recognize to be a straw-man argument. Not everyone who writes Python was hired for their ability to do it. Maybe the candidate is a stellar JavaScript developer, and their only Python weaknesses are with the syntax and standard library. Perhaps a cheat sheet is an effective way to bridge the gap between "learning" and "internalizing" a language's features.
Nonetheless, I'd like to hear people's thoughts on the hypothetical situation above (or another better one, if you feel the one I've chosen is biased or misses the point).