I think the small time difference you noticed is only due to method lookup.
Le mar. 3 déc. 2019 à 13:57, Kyle Stanley <aeros...@gmail.com> a écrit :
>
> > Actually there's no need to optimize the |= operator -- for strings we have
> > to optimize += *because* strings are immutable, but for dicts we would
> > define |= as essentially an alias for .update(), just like the relationship
> > between += and .extend() for lists, and then no unnecessary objects would
> > be created.
>
> Yeah that's why I noted that any form of optimization for the |= operator on
> dicts would not be the same as += is for strings. I wasn't actually sure of
> what form any potential optimization would take for the |= operator though.
> What exactly was the performance question/point in reference to? The question
> seemed to imply that there would be some minor performance detriment from
> using |=, but it's not clear to me as to when that would be a factor.
>
> > ## What about performance?
>
> > Performance is not the only objective when using Python. Switching to
> > inplace operators (here |=) is a generally useful and well-known technique
> > (it also applies to string and list concatenation, for example).
>
> Also with lists, I recall that using the += operator is very slightly faster
> than list.extend() in most situations:
>
> >>> ls_plus_eq = """\
> for i in range(1_000):
> ls += [x for x in range(10)]
> """
> >>> ls_extend = """\
> for i in range(1_000):
> ls.extend([x for x in range(10)])
> """
> >>> timeit.timeit(ls_plus_eq, setup="ls = []", number=10_000)
> 6.563132778996078
> >>> timeit.timeit(ls_extend, setup="ls = []", number=10_000)
> 6.695127692000824
> >>> timeit.timeit("ls+=other", setup="ls = []; other=[i for i in
> >>> range(100_000)]", number=10_000)
> 4.400735091003298
> >>> timeit.timeit("ls.extend(other)", setup="ls = []; other=[i for i in
> >>> range(100_000)]", number=10_000)
> 4.574331789997814
> >>> timeit.timeit("ls+=other", setup="ls = []; other=[i for i in
> >>> range(100)]", number=10_000_000)
> 3.5332175369985634
> >>> timeit.timeit("ls.extend(other)", setup="ls = []; other=[i for i in
> >>> range(100)]", number=10_000_000)
> 3.7756526679950184
>
> (Python 3.8)
>
> It seems to be a difference of only ~2-4% in most cases (~6-7% with the last
> set), but I find it interesting that += is barely faster. Of course, some of
> the above examples are fairly unrealistic, for most practical use cases
> they're essentially the same. I tend to prefer ls.extend() most of the time
> myself (the behavior is a bit more obvious). I'm mostly just curious if the
> difference between |= and dict.update() would end up being similar as far as
> performance goes, with |= having a negligible advantage over dict.update() in
> most situations.
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--
Antoine Rozo
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