Suppose you have an expensive calculation that gets used two or more times in a
loop. The obvious way to avoid calculating it twice in an ordinary loop is with
a temporary variable:
result = []
for x in data:
tmp = expensive_calculation(x)
result.append((tmp, tmp+1))
But what if you are using a list comprehension? Alas, list comps don't let you
have temporary variables, so you have to write this:
[(expensive_calculation(x), expensive_calculation(x) + 1) for x in data]
Or do you? ... no, you don't!
[(tmp, tmp + 1) for x in data for tmp in [expensive_calculation(x)]]
I can't decide whether that's an awesome trick or a horrible hack...
--
Steven
"Ever since I learned about confirmation bias, I've been seeing
it everywhere." - Jon Ronson
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