[Python-ideas] Add single() to itertools

Ivan Pozdeev vano at mail.mipt.ru
Mon Oct 30 05:49:09 EDT 2017

On 30.10.2017 9:29, python-ideas-request at python.org wrote:
> If I have understood your use-case, you have a function that returns a
> list of results (or possibly an iterator, or a tuple, or some other
> sequence):
>      print(search(haystack, needle))
>      # prints ['bronze needle', 'gold needle', 'silver needle']
> There are times you expect there to be a single result, and if there are
> multiple results, that is considered an error. Am I correct so far?
> If so, then sequence unpacking is your friend:
>      result, = search(haystack, needle)
> <...>
> I *think* this will solve your problem.
> If not, can you please explain what "single()" is supposed to do, why it
> belongs in itertools, and show an example of how it will work.
That works. Too arcane in my book though (and others' too according to 
https://stackoverflow.com/a/473337/648265), and the error messages are 
cryptic in this use case.
It also cannot be a part of an expression, unlike next().

The initial post on the above link summarizes the suggested 
implementation pretty well.


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