Will McGugan a écrit : > gabor wrote: > >> hi, >> >> there are 2 versions of a simple code. >> which is preferred? >> >> >> === >> if len(line) >= (n+1): >> text = line[n] >> else: >> text = 'nothing' >> === >> >> >> === >> try: >> text = line[n] >> except IndexError: >> text = 'nothing' >> === >> >> >> which is the one you would use? > > > I would actualy use the following for this particular case.. > > text = line[n:n+1] or 'nothing' ... and you would get either a list of one element or a string ... I think you wanted to write : text = (line[n:n+1] or ['nothing'])[0] However, I wouldn't use that because it is hard to read ... you have to know Python in great detail to know that: 1 - is the expressions "line[i:j]", i and j are replaced with "len(line)" if they are greater than "len(line)" 2 - so if n > len(line), then line[n:n+1]" == len[len(line):len(line)] == [] (it is not evident that line[n:n+1] can give an empty list ...) 3 - empty list evaluate to "False" 4 - the "or" operator returns the first argument evaluating to "true" So, in the end, you use 3 side-effects of Python in the same small expression ... (1, 2 and 4) > > But in general I think it is best to use exceptions like that only where > you expect the code to _not_ throw the exception the majority of times. > Otherwise the simple condition is better. Although I expect there is not > much difference either way.. > > > Will McGugan > -- > http://www.kelpiesoft.com What I would do is the following: - if this happen in a loop, I would, if possible, remove any test and catch the exception outside the loop ! - otherwise, I would go for the test, as it is more straitforward to read. Pierre
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