On 22Mar2020 05:09, Steven D'Aprano <st...@pearwood.info> wrote:
I agree with Ned -- whether the string object is returned unchanged or
a copy is an implementation decision, not a language decision.
[Eric]
The only reason I can think of is to enable the test above: did a
suffix/prefix removal take place? That seems like a useful thing.
We don't make this guarantee about string identity for any other string
method, and CPython's behaviour varies from method to method:
py> s = 'a b c'
py> s is s.strip()
True
py> s is s.lower()
False
and version to version:
py> s is s.replace('a', 'a') # 2.7
False
py> s is s.replace('a', 'a') # 3.5
True
I've never seen anyone relying on this behaviour, and I don't expect
these new methods will change that. Thinking that `is` is another way of
writing `==`, yes, I see that frequently. But relying on object identity
to see whether a new string was created by a method, no.
Well, ok, expressed on this basis, colour me convinced. I'm not ok with
not mandating that no change to the string returns an equal string (but,
really, _only_ because i can do a test with len(), as I consider a test
of content wildly excessive - potentially quite expensive - strings are
not always short).
If you want to know whether a prefix/suffix was removed, there's a more
reliable way than identity and a cheaper way than O(N) equality. Just
compare the length of the string before and after. If the lengths are
the same, nothing was removed.
Aye.
Cheers,
Cameron Simpson <c...@cskk.id.au>
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