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Groups > comp.lang.python > #30980

RE: Unpaking Tuple

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Thomas Bach wrote:
> Hi there,
> 
> On Sat, Oct 06, 2012 at 03:08:38PM +0000, Steven D'Aprano wrote:
> >
> > my_tuple = my_tuple[:4]
> > a,b,c,d = my_tuple if len(my_tuple) == 4 else (my_tuple + (None,)*4)[:4]
> >
> 
> Are you sure this works as you expect? I just stumbled over the following:
> 
> $ python
> Python 3.2.3 (default, Jun 25 2012, 23:10:56)
> [GCC 4.7.1] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
> >>> split = ['foo', 'bar']
> >>> head, tail = split if len(split) == 2 else split[0], None
> >>> head
> ['foo', 'bar']
> >>> tail
> >>>
> 
> I don't get it! Could someone help me, please? Why is head not 'foo'
> and tail not 'bar'?
> 
> Regards,
> 	Thomas
> --

I think you just need to wrap the else in parenthesis so the
else clause is treated as a tuple. Without the parenthesis 
I believe it is grouping the code like this.

head, tail = (split if len(split) == 2 else split[0] ), None

You want:
head, tail = split if len(split) == 2 else (split[0], None )


Ramit
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Unpaking Tuple sajuptpm <sajuptpm@gmail.com> - 2012-10-06 03:09 -0700
  Re: Unpaking Tuple Chris Rebert <clp2@rebertia.com> - 2012-10-06 03:27 -0700
    Re: Unpaking Tuple Roy Smith <roy@panix.com> - 2012-10-06 08:46 -0400
      Re: Unpaking Tuple Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-10-06 15:08 +0000
        Re: Unpaking Tuple Thomas Bach <thbach@students.uni-mainz.de> - 2012-10-08 23:45 +0200
        RE: Unpaking Tuple "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2012-10-08 22:21 +0000
          Re: RE: Unpaking Tuple Bob Martin <bob.martin@excite.com> - 2012-10-09 07:07 +0100
            Re: Unpaking Tuple Dave Angel <d@davea.name> - 2012-10-09 02:29 -0400
              Re: Unpaking Tuple Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2012-10-09 10:22 +0300
                Re: mangled messages (was: Unpaking Tuple) Tim Chase <python.list@tim.thechases.com> - 2012-10-09 05:48 -0500
                Re: mangled messages (was: Unpaking Tuple) Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2012-10-09 15:05 +0300
                Re: mangled messages Tim Chase <python.list@tim.thechases.com> - 2012-10-09 09:26 -0500
            Re: Unpaking Tuple Grant Edwards <invalid@invalid.invalid> - 2012-10-09 14:11 +0000
            RE: RE: Unpaking Tuple "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2012-10-09 16:40 +0000
            Re: Unpaking Tuple Robert Miles <robertmiles@teranews.com> - 2012-11-18 19:14 -0600
            Re: Unpaking Tuple Hans Mulder <hansmu@xs4all.nl> - 2012-11-19 02:56 +0100
  Re: Unpaking Tuple woooee <woooee@gmail.com> - 2012-10-07 10:58 -0700
    Re: Unpaking Tuple Terry Reedy <tjreedy@udel.edu> - 2012-10-07 16:03 -0400

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