On Tue, Oct 12, 2021 at 4:51 AM Chris Angelico <rosuav@gmail.com> wrote:
> Exactly: simple usage of next is often a bug. We need to be careful about this every time someone suggests that it's straight-forward to do next(iter(obj)).
<snip> 
Please give a real example of where calling first() and getting
ValueError is safer than calling next(iter(x)) and getting
StopIteration. So far, I am undeterred in believing that the two
exceptions have equivalent effect if the caller isn't expecting them.

I don't know about safer, but it is a clear example of why using next(iter(obj)) requires a pretty complete knowledge of the iteration protocol.

I can guarantee you I'd get some questions from my students when they got a StopIterationError!

If one DID write a first() function, it maybe or maybe not should raise a different exception, but it should certainly provide a better error message:

>>> next(iter([]))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration


Is not very helpful.

-CHB



 
ChrisA
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