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

[Stephen J. Turnbull]

Chris Barker writes:
 > On Mon, Mar 21, 2016 at 1:01 AM, Stephen J. Turnbull <stephen at xemacs.org>
 > wrote:
 > 
 > > AFAICS the OP's idea has a trivial and efficient expansion:
 > 
 > I'll take your word for it that this is efficient, and it is
 > trivial in amount of code to write, but it is not the least bit
 > trivial to read or write.

By "efficient" I mean only that the loop is unchanged.  Bonus is that
only one assignment and one test are needed outside of the loop.  The
only reason I could think of at the time that it might not be trivial
to read is that a reader is unfamiliar with the "sentinel = object()"
idiom.  Otherwise, "for" and "if" are the most basic of Python syntax,
so I felt safe in using that word.

Writing is another matter, but that's covered under the "sometimes ya
gotta be Dutch" clause. :-)

 > Howver, the motivating example was "the difference between *nothing**as
 > error* and *nothing** as really empty*, GUI/Web interfaces display an
 > explicit notice in case of empty lists to signify the correct execution of
 > a process/action/search or the other case."
 > 
 > Sure -- but this seem to be mixing validation with processing code -- you
 > really want to validate your inputs first.

If it's input, yes, but in my experience this would mostly be dealing
with internal state such as a database.  Then EAFP applies.  For
example, in paging, an empty page is a natural signal for end of
content.

 > AND: this would mostly be containers,

"Mostly", maybe, but that's not to say that iterators are an
unimportant case.  And if your application involves a mix of
containers and iterators, you may still prefer to use the same idioms
for both cases.

 > All that being said:
 > 
 > how about  "elempty"?, to go with elif?

-1 Not to my taste, to say the least.