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When I see a list comprehension I can see with a single glance what it's doing. Not so with the 4 line for loop. Comprehensions aren't a strange language featur
by jules 12y ago
When I see a list comprehension I can see with a single glance what it's doing. Not so with the 4 line for loop. Comprehensions aren't a strange language feature in Python either...it's one of the central features of Python.
Don't use something until it's proven to yield a great benefit is a very conservative approach. That may be appropriate in some cases, but I'm very glad that I am not in such a team since that would be incredibly frustrating. I much prefer an approach where you go with the choice that's most likely the better one, even if it's not 100% proven better or not a big difference.
- sophacles 12y agoI'm talking strictly about multi "for" comprehensions. They just are too confusing to me and most of the people I've worked with ever. But we also use lots (most) python features fully, just that one has been the source of dozens of bugs in this one codebase, not to mention others I've worked on with other people. It is a shitty non-intuitive syntax. Nested for loops, flatten(), various itertools functions and chained generator expressions all suffice, and I have yet to see them provide measurable slowdown to actual code compared to good algorithms and decent factoring. Like I said, I'll even use multi-for comprehensions if there is a measurable difference over nested for-loops. Also, I think you are intentionally misrepresenting what I said - when I said don't use "weird stuff" I explicitly excluded idiomatic language things. That includes (for python) single for comprehensions. The multi-for comprehension is something I rarely come across in the wild despite it's long time existence in python - it's a weird one.
- hueving 12y agoI think you are trying to justify your strange preferences after the fact. How exactly were there bugs caused by nested for loops that you encountered? It's not like if you mess up the order it will actually run without throwing an exception. Nested list comprehensions are idiomatic python. It's really strange that you don't let your team use them because you are afraid of them.
- jevgeni 12y agoWell, Google doesn't recommend it either (http://google-styleguide.googlecode.com/svn/trunk/pyguide.html?showone=List_Comprehensions#List_Comprehensions http://google-styleguide.googlecode.com/svn/trunk/pyguide.ht...), but I guess they are all bloody noobs or whatever. I mean, single level comprehension is good. Nested list comprehension is OK only in most trivial cases. In my opinion, if I see how a person uses list comprehension, I can tell, what kind of person this is. There are people who, for example, do this def all_is_okey_dorey(lst): return all([some_predicate_fn(x) for x in lst]) instead of this def all_is_okey_dorey(lst): for x in lst: if not some_predicate_fn(x): return False return True and can live with themselves somehow. Or there are people, who refuse to acknowledge the existence of anything besides Python 3.x and when forced to write in 2.x use list comprehension instead of iterator comprehension. Thing is, the validity of using nested list comprehension depends not on the amount of for loops you have, but on the thing you want to do with the item. If it's just selection, then it might be ok. If you want to apply some kind of function to it, then it's most probably the case of trying to be too clever.
- jules 12y agoThe only thing wrong with that list comprehension version is those [ ] all(some_predicate_fn(x) for x in lst) Much better than the loop.
- hueving 12y agoIf you think two loops is not a "simple case" of a list comprehension as Google suggests to use them for, perhaps you shouldn't be doing code reviews. It sounds like your team would be held down by your weak grasp of the language.