Re: Loop with else clause
DL Neil writes:
> 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...
(As an aside: It's best to avoid choosing names like ‘list’ that clobber
built-in names; your code examples are harder to read that way. I'll
assume a different name, ‘ipsums’.)
One aspect of that example I would prefer to avoid: It scatters the
handling of the list to different locations in the code. It's not
obvious from the purpose of ‘process_list’ whether that function should
be handling an empty list; this could lead to double-handling in
different locations.
An alternative to consider::
if ipsums:
for item in ipsums:
process_item(item)
else:
print("Sorry...")
An advantage of this is that the handling of the list is all in the same
place, where changing that logic later will be easier. The
‘process_item’ then just assumes some other code has decided which items
to handle; it becomes correspondingly simpler.
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_o__) 1999 |
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Re: Loop with else clause
DL Neil wrote:
> 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?
> 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!
An argument in favour of the flag is that it works with arbitrary iterables
whereas if ...: fails:
>>> numbered = enumerate([])
>>> if numbered:
... print("the winners are")
... for ix in numbered: print(*ix)
...
the winners are
> The ideas went (rapidly) down-hill from there...
>
>
> Is there another, more pythonic, approach to conditional (for/while)
> loop processing?
I'm not aware of such an approach.
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Re: python is going to die! =(
python is alive -- https://mail.python.org/mailman/listinfo/python-list
Re: python is going to die! =(
Python is the only immortal On Tue, 5 Feb 2019, 17:01 python is alive > -- > https://mail.python.org/mailman/listinfo/python-list > -- https://mail.python.org/mailman/listinfo/python-list
Re: Python program to phone?
see pydroid and qpython on play store.2 Abdur-Rahmaan Janhangeer http://www.pythonmembers.club | https://github.com/Abdur-rahmaanJ Mauritius -- https://mail.python.org/mailman/listinfo/python-list
Re: Python program to phone?
On 04/02/2019 23:12, Chris Roy-Smith wrote: On 5/2/19 7:20 am, Steve wrote: P.S. Yes, I tried to post this about two weeks ago but could not seem to respond to the replies I received. I could contact one or two individuals but apparently not the masses. How do I find out how this list works? Hi Steve, to reply to the newsgroup use "followup" NOT "reply" If you're using the mailing list rather than the newsgroup, reply to the list (python-list@python.org) instead of the Reply-To address. Most mail programs have an appropriate reply option: on Thunderbird it's the "Reply List" button. Sorry I can't help you on your initial problem Likewise :-( -- Rhodri James *-* Kynesim Ltd -- https://mail.python.org/mailman/listinfo/python-list
Re: Python program to phone?
Hi there Steve. Did you check BeeWare? (https://pybee.org/) -- https://mail.python.org/mailman/listinfo/python-list
RE: Loop with else clause
As mentioned somewhere, "readability counts", so why not just go with exactly
what you said...
if len(nominees) > 0:#if a condition exists
for nominee in nominees: #the loop should be executed
print(nominee)
else:#but if not
print("D'oh! No one is worthy.") #something else should be done
The fancy features of the language can be cool and all, but forcing yourself to
use them just for the sake of using them and "being pythonic" can result in
weird situations, and wrong or unclear assumptions or intents. When someone
else reads it later it may hide what you were actually intending the check to
look for.
Hmm, "if nominees:" Did they make it like that to look for a 0 length list, or
to make sure they didn't get None by accident, or both, or something different?
Hmm, "if len(nominees) > 0:" Ahh ok, we want to make sure there's something in
there.
So my 2 cents: Feel free to be non-pythonic if it makes things clear and works.
-Original Message-
From: Python-list
[mailto:python-list-bounces+david.raymond=tomtom@python.org] On Behalf Of
Peter Otten
Sent: Tuesday, February 05, 2019 3:44 AM
To: python-list@python.org
Subject: Re: Loop with else clause
DL Neil wrote:
> 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?
> 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!
An argument in favour of the flag is that it works with arbitrary iterables
whereas if ...: fails:
>>> numbered = enumerate([])
>>> if numbered:
... print("the winners are")
... for ix in numbered: print(*ix)
...
the winners are
> The ideas went (rapidly) down-hill from there...
>
>
> Is there another, more pythonic, approach to conditional (for/while)
> loop processing?
I'm not aware of such an approach.
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Re: Loop with else clause
I don't know if it is very Pythonic, but I would do something like
if no_oscar_nominees:
print ("Sorry ...")
else:
print_list_of_oscar_nominees()
And yes, that for/else construct can be confusing.
Adriaan.
>>> On 5-2-2019 at 5:29, DL Neil
wrote:
> 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?
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RE: Loop with else clause
The topic is how to deal with a python loop that may not be run if you want something else to happen in that case. Multiple solutions are presented along with this request: > Is there another, more pythonic, approach to conditional (for/while) > loop processing? Has anyone considered looking at this from the perspective of the CONDITION being evaluated? If the condition is something simple like is the "list" empty, then any method will work as it can be evaluated before trying the loop with no side effects. But what if the item in question is complex and constructed dynamically as by zipping things together or calling functions and might even produce side effects? It might be far from trivial to do that before the loop and check and you might inadvertently change things. Using a sentinel approach might be safer. And what about loops that start but exit immediately without doing anything? If you iterate on something whose first value is wrong in some way and the loop starts with an "if ... break" then do you want to do the ELSE condition because the loop sort of did not run as anticipated? A similar example is if the loop starts with a "try" and the error handler does a break. -- https://mail.python.org/mailman/listinfo/python-list
Re: Loop with Else Clause
-Original Message- From: Python-list On Behalf Of DL Neil Sent: Monday, February 4, 2019 11:29 PM To: 'Python' 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? -- Just reading this by itself without seeing the illustrative problem, my first gut reaction was "while loop!" but then it became more obvious that this was a one-off condition to decide to get started, as opposed to being the loop condition itself. That being said, I would agree that you really cannot do better than the if-else already presented, since it is clearly a binary choice: execute the complete loop, or don't if you can't. I personally try to avoid the else part on both while loops and for loops because of this sort of confusion. All other things being equal, having an else section is fundamentally the same thing as simply omitting the 'else:' and out-denting the consequence, and makes it very clear just what is going on. The difference, of course, appears when you have a 'break' within that loop that exits prematurely. And that's where the structured-programming purist in me starts to gibber in fear and loathing. My purist self says that if 'break' is applicable, than exception handling is just as applicable with a much cleaner model, since you can control where to go next, whether to continue repeating, etc. If I don't expect to get all the way through a for loop, I simply don't write a for loop -- I'll substitute with a while, moving the logical negation of the break condition into the while loop condition, making it very clear that I don't plan to make it to the end. Unfortunately, the for loop is such a common Pythonic thing to do that I really can't say 'for/break' is unPythonic -- I can only substitute Lovecraftian adjectives (in my opinion, of course) to describe that construct. But this whole little tangent of mine doesn't seem to apply to your situation at all, and I don't there is a 'single' language element in any programming language I can think of that does what you ask -- so stick with the cleaner: if (__): # loop; else: #don't loop Roger Christman Pennsylvania State University -- https://mail.python.org/mailman/listinfo/python-list
Re: Implement C's Switch in Python 3
On Saturday, February 2, 2019 at 6:47:49 PM UTC-6, Sayth Renshaw wrote:
> Hi
>
> I am trying to convert a switch statement from C into Python. (why?
> practising).
>
> This is the C code.
>
> printf("Dated this %d", day);
> switch (day) {
> case 1: case 21: case 31:
> printf("st"); break;
> case 2: case 22:
> printf("nd"); break;
> case 3: case 23:
> printf("rd"); break;
> default: printf("th"); break;
>
> }
> printf(" day of ");
>
> #Premise if the use enter an int as the date 21 for example it would print
> 21st. It appends the correct suffix onto a date.
>
> Reading and trying to implement a function that uses a dictionary. Not sure
> how to supply list into it to keep it brief and with default case of 'th'.
>
> This is my current code.
>
> def f(x):
> return {
> [1, 21, 31]: "st",
> [2, 22]: "nd",
> [3, 23]: "rd",
> }.get(x, "th")
>
>
> print(f(21))
>
> I have an unhashable type list. Whats the best way to go?
>
> Cheers
>
> Sayth
My best, readable attempt good for 1 - 99:
def sufx( day ):
if (day % 10) in [0,4,5,6,7,8,9] or (day / 10) == 1:
return 'th'
return {1: 'st', 2: 'nd', 3: 'rd'}[day % 10]
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Re: Implement C's Switch in Python 3
On 2019-02-06 00:25, John Sanders wrote:
On Saturday, February 2, 2019 at 6:47:49 PM UTC-6, Sayth Renshaw wrote:
Hi
I am trying to convert a switch statement from C into Python. (why? practising).
This is the C code.
printf("Dated this %d", day);
switch (day) {
case 1: case 21: case 31:
printf("st"); break;
case 2: case 22:
printf("nd"); break;
case 3: case 23:
printf("rd"); break;
default: printf("th"); break;
}
printf(" day of ");
#Premise if the use enter an int as the date 21 for example it would print
21st. It appends the correct suffix onto a date.
Reading and trying to implement a function that uses a dictionary. Not sure how
to supply list into it to keep it brief and with default case of 'th'.
This is my current code.
def f(x):
return {
[1, 21, 31]: "st",
[2, 22]: "nd",
[3, 23]: "rd",
}.get(x, "th")
print(f(21))
I have an unhashable type list. Whats the best way to go?
Cheers
Sayth
My best, readable attempt good for 1 - 99:
def sufx( day ):
if (day % 10) in [0,4,5,6,7,8,9] or (day / 10) == 1:
return 'th'
return {1: 'st', 2: 'nd', 3: 'rd'}[day % 10]
In Python 3, 11/10 == 1.1, not 1.
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