Question

It seems silly to write the following:

L = []

if x in L:
  L[x] = something
else:
  L[x] = something_else

Doesn’t this perform the look-up for x twice? I tried using index(), but this gives an error when the value is not found.

Ideally I would like to say like:

if x is in L, save that index and:
  ...

I can appreciate that this might be a beginner python idiom, but it seems rather un-search-able. Thanks.

Answer 1

Another option is try/except:

d = {}
try:
    d[x] = something_else
except KeyError:
    d[x] = something

Same result as your code.

Edit: Okay, fast moving target. Same idiom for a list, different exception (IndexError).