I think the small time difference you noticed is only due to method lookup.
Le mar. 3 déc. 2019 à 13:57, Kyle Stanley <email@example.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)
> >>> timeit.timeit(ls_extend, setup="ls = ", number=10_000)
> >>> timeit.timeit("ls+=other", setup="ls = ; other=[i for i in range(100_000)]", number=10_000)
> >>> timeit.timeit("ls.extend(other)", setup="ls = ; other=[i for i in range(100_000)]", number=10_000)
> >>> timeit.timeit("ls+=other", setup="ls = ; other=[i for i in range(100)]", number=10_000_000)
> >>> timeit.timeit("ls.extend(other)", setup="ls = ; other=[i for i in range(100)]", number=10_000_000)
> (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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