Coding style

[PTY]

Which is better?

lst = [1,2,3,4,5]

while lst:
lst.pop()

OR

while len(lst) 0:
lst.pop()

[Simon Brunning]

Re: Coding style

On 17 Jul 2006 08:56:34 -0700, PTY <ty.2006@yahoo. comwrote:

Which is better?
>
lst = [1,2,3,4,5]
>
while lst:
lst.pop()
>
OR
>
while len(lst) 0:
lst.pop()

How about:

lst = [1,2,3,4,5]
while lst:
lst.pop()

Or even just:

lst = []

;-)

--
Cheers,
Simon B,
simon@brunningo nline.net,

http://www.brunningonline.net/simon/blog/

[Steve Holden]

Re: Coding style

PTY wrote:

Which is better?
>
lst = [1,2,3,4,5]
>
while lst:
lst.pop()
>
OR
>
while len(lst) 0:
lst.pop()
>

The former, without a doubt. It says exactly the same thing, since lst
can only be considered false when it is empty. Experienced Python
programmers would scratch their heads at your second formulation.

I doubt there's much in it from a time point of view (though I know as I
write this it will spur someone to use timeit.py to point out I am wrong).

regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://holdenweb.blogspot.com
Recent Ramblings http://del.icio.us/steve.holden

[Tim Chase]

Re: Coding style

lst = [1,2,3,4,5]

while lst:
lst.pop()
>
Or even just:
>
lst = []

Subtly different though...

>>while lst:

.... lst.pop()
....
5
4
3
2
1

>>lst2

[]

>>lst = [1,2,3,4,5]
>>lst2 = lst
>>lst = []
>>lst2

[1, 2, 3, 4, 5]

>>lst = [1,2,3,4,5]
>>lst2 = lst
>>del lst[:]
>>lst2

[]

The original while loop changes the actual list, reassigning it
to a new list prevents other items that reference that list from
accessing the changes. As shown above, I recommend

del lst[:]

which should be as fast as python will let one do it. (maybe?
again with those timeit guys... ;)

-tkc

[tac-tics]

Re: Coding style

Or even just:

>
lst = []
>
;-)

Indeed.

I'd say the second one. Empty lists are not false. They are empty. Long
live dedicated boolean data types.

[dwelch91]

Re: Coding style

PTY wrote:

Which is better?
>
lst = [1,2,3,4,5]
>
while lst:
lst.pop()
>
OR
>
while len(lst) 0:
lst.pop()
>

I think the first one is better, but if all you are doing is removing
all the items in the list, this is definitely better:

lst = []

-Don

[Steve Holden]

Re: Coding style

tac-tics wrote:

>>Or even just:
>>
>>lst = []
>>
>>;-)

>
>
Indeed.
>
I'd say the second one. Empty lists are not false. They are empty. Long
live dedicated boolean data types.
>

Take them off to where they belong!

I'll bet you still write

if a>3 == True:

don't you ;-)

regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://holdenweb.blogspot.com
Recent Ramblings http://del.icio.us/steve.holden

[dwelch91]

Re: Coding style

tac-tics wrote:

>
I'd say the second one. Empty lists are not false. They are empty. Long
live dedicated boolean data types.
>

Uh, no, empty lists are False in a boolean context:

http://docs.python.org/lib/truth.html

-Don

[Peter Otten]

Re: Coding style

Steve Holden wrote:

I'll bet you still write
>
if a>3 == True:
>
don't you ;-)

I'll second that.

if (a>3) == True:

is the correct way :-)

Peter

[Dave Hansen]

Re: Coding style

On Mon, 17 Jul 2006 17:09:32 +0100 in comp.lang.pytho n, "Simon
Brunning" <simon@brunning online.netwrote :

[...]

>
>lst = [1,2,3,4,5]
>while lst:
lst.pop()
>
>Or even just:
>
>lst = []
>

del lst[:]

is probably closer to what the OP wants...

Regards,
-=Dave

--
Change is inevitable, progress is not.

[Roger Miller]

Re: Coding style

Peter Otten wrote:

Steve Holden wrote:
>

I'll bet you still write

if a>3 == True:

don't you ;-)

>
I'll second that.
>
if (a>3) == True:
>
is the correct way :-)
>
Peter

No, to be consistent you'll have to write

if ((a>3) == True) == True:

Oops, I mean,

if (((a>3) == True) == True) == True:

Umm, never mind.

[rurpy@yahoo.com]

Re: Coding style

PTY wrote:

Which is better?
>
lst = [1,2,3,4,5]
>
while lst:
lst.pop()
>
OR
>
while len(lst) 0:
lst.pop()

A dozen posts, but nobody has posted the right
answer yet, so I will :-)

It doesn't matter -- use whichever you prefer (*)
This is an angels on the head of a pin issue.

(*) -- If your code is part of an existing body of
code that uses one or the other style consistently,
then you should do the same.

[Donn Cave]

Re: Coding style

In article <mailman.8257.1 153158306.27775 .python-list@python.org >,
Steve Holden <steve@holdenwe b.comwrote:

tac-tics wrote:

....

>I'd say the second one. Empty lists are not false. They are empty.
>Long live dedicated boolean data types.

Take them off to where they belong!

Tac-tics is right, an empty list is not False.

Anyway, just for some variety, I think (2) is preferrable
to (1), as is the following

while 1:
try:
lst.pop()
except IndexError:
break

Rather than blindly apply familiar patterns to our work,
I think everyone would agree that coding style in matters
like this should follow the underlying point of the code.
In this case, the body of the test refers implicitly to
the length of the list, since .pop() -(list[a], list[:a])
where a is (len(list) - 1) It's therefore quite appropriate
for the test to be length.

Donn Cave, donn@u.washingt on.edu

[Erik Max Francis]

Re: Coding style

Donn Cave wrote:

Tac-tics is right, an empty list is not False.

But that's not what he said. He said it was "not false." That's wrong.
It's false. It's just not False.

--
Erik Max Francis && max@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
The meaning of life is that it stops.
-- Franz Kafka

[Bob Greschke]

Re: Coding style


<rurpy@yahoo.co mwrote in message
news:1153168968 .995422.198360@ m73g2000cwd.goo glegroups.com.. .

PTY wrote:

>Which is better?
>>
>lst = [1,2,3,4,5]
>>
>while lst:
> lst.pop()
>>
>OR
>>
>while len(lst) 0:
> lst.pop()

>
A dozen posts, but nobody has posted the right
answer yet, so I will :-)
>
It doesn't matter -- use whichever you prefer (*)
This is an angels on the head of a pin issue.
>
(*) -- If your code is part of an existing body of
code that uses one or the other style consistently,
then you should do the same.
>

I'd go even one step further. Turn it into English (or your favorite
non-computer language):

1. While list, pop.

2. While the length of the list is greater than 0, pop.

Which one makes more sense? Guess which one I like. CPU cycles be damned.
:)

Bob