[Python-ideas] Control Flow - Never Executed Loop Body

[Sven R. Kunze]

On 21.03.2016 21:57, Vito De Tullio wrote:
> Chris Angelico wrote:
>>
>> What if 'iterable' is locals().values()? Can you, with perfect
>> reliability, recognize that case? AIUI this is exactly why next() and
>> __next__() are defined to "return a value or raise", rather than
>> "return a value or return a magic no-more-values value", because
>> there's always the possibility that the no-more-values value is a
>> legitimately-yielded value.
> so, the "correct" way to handle this is something like
>
>      try:
>          e = next(iterable)
>      except StopIteration:
>          empty_suite()	# there is no element
>      else:
>          main_suite(e)	# handle the first element
>          for e in iterable:
>              main_suite(e)	# handle the rest of the elements
>
> ?
>
> apart for the readability you need to "copy" the same code two times (or
> refactor in a function)

Interesting. I didn't think of this solution.

However, I assume that when I do "object()" I got something unique among 
all other objects. So,

item = sentinel = object()
for item in collection:
     main_suite(item)
if item is sentinel:
     empty_suite()

Is still quite correct, right?

Best,
Sven