[Scons-users] Is this a feature or a bug
(

[Kenny, Jason L]

I believe the issue as I see it here is that SCon has API, that would like to have overloading. Ie one case that takes a string and another that takes a collection of strings ( be that a set or list or tuple)

The way SCons is dealing with this is via a type check, which seems to be the python way, as we don’t have any other way to do this.

This could be fixed by always taking a set of strings, But this still requires a check to see if this is a string, otherwise there is no good way to report a useful error to the user.

Jason

From: scons-users-bounces at scons.org [mailto:scons-users-bounces at scons.org] On Behalf Of Kyle J Strand
Sent: Tuesday, August 21, 2012 3:59 PM
To: SCons users mailing list
Cc: scons-users at scons.org; scons-users-bounces at scons.org
Subject: Re: [Scons-users] Is this a feature or a bug(

I agree that from a user perspective, the third argument should be any iterable, but I'd be willing to bet that the tuple is in fact being turned into a single-item list somewhere in the code. This is a hazard of the "if not isinstance(inputarg, list): inputarg = [inputarg]" pattern that seems to show up a lot in the SCons code (and arguably a hazard of ever using "isinstance"). While this is certainly a very Pythonic issue to be running into, I don't think it would be "unPythonic" in the least to fix it. But that might be a question better suited to the dev list.

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Kyle Strand, Software Intern
Beckman Coulter, Inc., Life Sciences Division
4862 Innovation Drive, Fort Collins, Colorado, 80525
(970) 204-7036

scons-users-bounces at scons.org<mailto:scons-users-bounces at scons.org> wrote on 08/21/2012 01:14:48 PM:


> William Deegan <bill at baddogconsulting.com<mailto:bill at baddogconsulting.com>>

> Sent by: scons-users-bounces at scons.org<mailto:scons-users-bounces at scons.org>

>

> 08/21/2012 01:14 PM

>

> Please respond to

> SCons users mailing list <scons-users at scons.org<mailto:scons-users at scons.org>>

>

> To

>

> scons-users at scons.org<mailto:scons-users at scons.org>

>

> cc

>

> Subject

>

> Re: [Scons-users] Is this a feature or a bug…

>

> On 08/21/2012 08:40 AM, Chris BeHanna wrote:

> > On Aug 21, 2012, at 10:04 , Gary Oberbrunner <garyo at oberbrunner.com<mailto:garyo at oberbrunner.com>> wrote:

> >

> >> On Tue, Aug 21, 2012 at 10:44 AM, Russel Winder

> <russel at winder.org.uk<mailto:russel at winder.org.uk>> wrote:

> >>> Just asking the question prior to putting in a bug report, just in case

> >>> I have missed something…

> >>>

> >>> Command(XXX, YYY, [AAA, BBB])

> >>>

> >>> i.e. the action sequence is a list, works fine.  However,

> >>>

> >>> Command(XXX, YYY, (AAA, BBB))

> >>>

> >>> is reported as an error, i.e. a tuple is not acceptable where a list is.

> >>>

> >>> To say this doesn't violate the Principle of Least Surprise would be to

> >>> violate the Principle of Least Surprise.

> >> I can't see any particular reason we shouldn't support tuples as well

> >> as lists there, although actually doing it might be complicated.

> >    A tuple, strictly speaking, is not *exactly* the same as a list

> in python.  What you might have happen is this:

> >

> >    Command(XXX, YYY, (AAA, BBB))

> >

> > gets translated by layers below as

> >

> >    Command(XXX, YYY, [(AAA,BBB)])

> >

> > i.e., that tuple becomes a singleton dictionary with a single key-

> value pair, rather than a list with two elements.

> >

> >    Thus, I would disagree, looking at it from a strictly

> "pythonic" view, that it violates POLA.  I would actually expect it

> not to work properly.

> >

> Likely the third argument should allow any iterable.

> So it could be a generator even.

> The contents of a single element would be what you'd then have to check

> to see if they matched what was expected. (To address your [(aaa,bbb)]

> above.)

>

>

> -Bill

>

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