> 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?

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.