On 5/02/19 8:12 PM, Steve wrote:
Would it be a hyphythonitical question?
Is that one of the new meta-classes in release 3.99, or a perhaps a
project to remove the GIL and take advantage of multi-core architectures?
As well as embarrassing the poor coder, this question vexed quite a few
minds this afternoon (even allowing for the gathering mood - tomorrow
being a public holiday!).
Even though it seemed so straightforward to me, others felt it
reasonable that there would be some way to tell that a loop never
executed - there must be a simpler, more pythonic, construct...
=================
Footnote:
Zamboni locks up after running into large patch of loose teeth.
-----Original Message-----
From: Python-list <python-list-bounces+gronicus=sga.ni...@python.org> On
Behalf Of DL Neil
Sent: Monday, February 4, 2019 11:29 PM
To: 'Python' <python-list@python.org>
Subject: Loop with else clause
What is the pythonic way to handle the situation where if a condition exists
the loop should be executed, but if it does not something else should be
done?
Why am I asking?
Today's code review included a for...else structure. I've rarely seen such a
thing, and even knowing it exists, cannot recall ever using it!
The coder intended to implement the scenario (above) but did not realise
that the else-clause means 'execute if the loop ended without using break'.
She thought it meant 'if there's nothing in the iterable, execute the else
clause' (per if...then...else... ie the two clauses are
mutually-exclusive*) - which one assumes is the reason why the BDfL is
claimed to have said it should never have been implemented (this way).
She neglected to test the exception properly, and was lulled into a false
sense of security by the coverage reporting 100%. Oops!
*see also the more commonly-used try...except...else...[finally...]
When/how does this occur?
Our client is more than a little commercially-sensitive. So as a really
simple scenario, imagine a report is required, naming people who have become
eligible for something, eg students qualified to enter an advanced class,
Oscar film award nominees, entrants who have fulfilled the requirements of a
competition from which a winner will be randomly selected...
The names all appear in a list, so the most frequent use-case is trivial:
print( "And the winners are:" )
for name in list:
print( name )
but, if no-one actually qualifies, a warning message is required, eg
print( "Sorry, no-one is eligible" )
Possible solution:
To make anything more than the trivial case readable, I think I'd put the
list processing into one function, and the exception into another (except
that this case is so trivial), ie
if list:
process_list() #the heading and for-loop, as above
else:
print( "Sorry...
Others wanted to add a semaphore/flag inside the loop to indicate if it was
executed at least once. Yes, could even use the else clause then!
The ideas went (rapidly) down-hill from there...
Is there another, more pythonic, approach to conditional (for/while) loop
processing?
--
Regards,
=dn
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Regards =dn
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