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Most probably a stupid question, but I still want to ask

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  Most probably a stupid question, but I still want to ask Fillmore <fillmore_remove@hotmail.com> - 2016-04-10 18:51 -0400
    Re: Most probably a stupid question, but I still want to ask Chris Angelico <rosuav@gmail.com> - 2016-04-11 08:58 +1000
    Re: Most probably a stupid question, but I still want to ask Ben Finney <ben+python@benfinney.id.au> - 2016-04-11 09:04 +1000
    Re: Most probably a stupid question, but I still want to ask Stephen Hansen <me+python@ixokai.io> - 2016-04-10 16:30 -0700
      Re: Most probably a stupid question, but I still want to ask Fillmore <fillmore_remove@hotmail.com> - 2016-04-10 20:17 -0400
        Re: Most probably a stupid question, but I still want to ask Stephen Hansen <me+python@ixokai.io> - 2016-04-10 17:32 -0700
        Re: Most probably a stupid question, but I still want to ask Terry Reedy <tjreedy@udel.edu> - 2016-04-10 21:45 -0400
          Re: Most probably a stupid question, but I still want to ask Marko Rauhamaa <marko@pacujo.net> - 2016-04-11 08:41 +0300
    one-element tuples [Was: Most probably a stupid question, but I still want to ask] Fillmore <fillmore_remove@hotmail.com> - 2016-04-10 20:13 -0400
      Re: one-element tuples [Was: Most probably a stupid question, but I still want to ask] Stephen Hansen <me+python@ixokai.io> - 2016-04-10 17:19 -0700
      Re: one-element tuples [Was: Most probably a stupid question, but I still want to ask] Stephen Hansen <me+python@ixokai.io> - 2016-04-10 17:18 -0700
      Re: one-element tuples [Was: Most probably a stupid question, but I still want to ask] Chris Angelico <rosuav@gmail.com> - 2016-04-11 10:20 +1000
      Re: one-element tuples [Was: Most probably a stupid question, but I still want to ask] Fillmore <fillmore_remove@hotmail.com> - 2016-04-10 20:22 -0400
        Re: one-element tuples [Was: Most probably a stupid question, but I still want to ask] Stephen Hansen <me+python@ixokai.io> - 2016-04-10 17:28 -0700
        Re: one-element tuples Ben Finney <ben+python@benfinney.id.au> - 2016-04-11 10:31 +1000
          Re: one-element tuples Fillmore <fillmore_remove@hotmail.com> - 2016-04-10 20:48 -0400
            Re: one-element tuples Ben Finney <ben+python@benfinney.id.au> - 2016-04-11 10:56 +1000
              Re: one-element tuples Grant Edwards <invalid@invalid.invalid> - 2016-04-11 14:10 +0000
                Re: one-element tuples Fillmore <fillmore_remove@hotmail.com> - 2016-04-11 10:11 -0400
                  Re: one-element tuples Grant Edwards <invalid@invalid.invalid> - 2016-04-11 14:26 +0000
            Re: one-element tuples Ned Batchelder <ned@nedbatchelder.com> - 2016-04-10 18:00 -0700
            Re: one-element tuples Stephen Hansen <me+python@ixokai.io> - 2016-04-10 18:07 -0700
            Re: one-element tuples "Martin A. Brown" <martin@linux-ip.net> - 2016-04-10 18:08 -0700
              Re: one-element tuples Fillmore <fillmore_remove@hotmail.com> - 2016-04-10 23:19 -0400
                Re: one-element tuples Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-04-11 09:57 +0300
                Re: one-element tuples Larry Hudson <orgnut@yahoo.com> - 2016-04-11 23:01 -0700
            Re: one-element tuples Ben Finney <ben+python@benfinney.id.au> - 2016-04-11 11:36 +1000
              Re: one-element tuples Fillmore <fillmore_remove@hotmail.com> - 2016-04-10 22:57 -0400
                Re: one-element tuples Ben Finney <ben+python@benfinney.id.au> - 2016-04-11 14:10 +1000
                  Re: one-element tuples Fillmore <fillmore_remove@hotmail.com> - 2016-04-11 00:43 -0400
                    Re: one-element tuples Stephen Hansen <me+python@ixokai.io> - 2016-04-10 21:54 -0700
                    Re: one-element tuples Ben Finney <ben+python@benfinney.id.au> - 2016-04-11 15:40 +1000
                  Re: one-element tuples Rustom Mody <rustompmody@gmail.com> - 2016-04-10 22:07 -0700
            Re: one-element tuples BartC <bc@freeuk.com> - 2016-04-11 12:15 +0100
              Re: one-element tuples Marko Rauhamaa <marko@pacujo.net> - 2016-04-11 15:12 +0300
                Re: one-element tuples Grant Edwards <invalid@invalid.invalid> - 2016-04-11 14:12 +0000
      Re: one-element tuples [Was: Most probably a stupid question, but I still want to ask] Ben Finney <ben+python@benfinney.id.au> - 2016-04-11 10:30 +1000
      Re: one-element tuples [Was: Most probably a stupid question, but I still want to ask] MRAB <python@mrabarnett.plus.com> - 2016-04-11 01:33 +0100
        Re: one-element tuples [Was: Most probably a stupid question, but I still want to ask] Dan Sommers <dan@tombstonezero.net> - 2016-04-11 02:22 +0000
          Re: one-element tuples [Was: Most probably a stupid question, but I still want to ask] Chris Angelico <rosuav@gmail.com> - 2016-04-11 12:34 +1000
      Re: one-element tuples [Was: Most probably a stupid question, but I still want to ask] Chris Angelico <rosuav@gmail.com> - 2016-04-11 10:38 +1000
      Parens do create a tuple (was: one-element tuples [Was: Most probably a stupid question, but I still want to ask]) Ben Finney <ben+python@benfinney.id.au> - 2016-04-11 10:45 +1000
      Re: Parens do create a tuple (was: one-element tuples [Was: Most probably a stupid question, but I still want to ask]) Chris Angelico <rosuav@gmail.com> - 2016-04-11 10:50 +1000
      Re: Parens do create a tuple Ben Finney <ben+python@benfinney.id.au> - 2016-04-11 10:57 +1000
      Re: Parens do create a tuple Chris Angelico <rosuav@gmail.com> - 2016-04-11 11:04 +1000
      Re: Parens do create a tuple (was: one-element tuples [Was: Most probably a stupid question, but I still want to ask]) Stephen Hansen <me@ixokai.io> - 2016-04-10 18:03 -0700
      Re: Parens do create a tuple (was: one-element tuples [Was: Most probably a stupid question, but I still want to ask]) Tim Chase <python.list@tim.thechases.com> - 2016-04-10 19:52 -0500
      Re: Parens do create a tuple Ben Finney <ben+python@benfinney.id.au> - 2016-04-11 11:41 +1000
        Re: Parens do create a tuple Steven D'Aprano <steve@pearwood.info> - 2016-04-11 12:32 +1000
          Re: Parens do create a tuple Random832 <random832@fastmail.com> - 2016-04-10 22:51 -0400
            Re: Parens do create a tuple Steven D'Aprano <steve@pearwood.info> - 2016-04-11 14:08 +1000
              Re: Parens do create a tuple Random832 <random832@fastmail.com> - 2016-04-11 01:27 -0400
                Re: Parens do create a tuple Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-04-11 18:01 +1000
                  Re: Parens do create a tuple Random832 <random832@fastmail.com> - 2016-04-11 09:42 -0400
          Re: Parens do create a tuple Chris Angelico <rosuav@gmail.com> - 2016-04-11 13:02 +1000
          Re: Parens do create a tuple Ben Finney <ben+python@benfinney.id.au> - 2016-04-11 14:08 +1000
      Re: Parens do create a tuple Chris Angelico <rosuav@gmail.com> - 2016-04-11 11:51 +1000
        Re: Parens do create a tuple Steven D'Aprano <steve@pearwood.info> - 2016-04-11 12:57 +1000
      Re: one-element tuples [Was: Most probably a stupid question, but I still want to ask] Tim Chase <python.list@tim.thechases.com> - 2016-04-10 19:46 -0500
    Re: Most probably a stupid question, but I still want to ask Steven D'Aprano <steve@pearwood.info> - 2016-04-11 11:50 +1000
      Re: Most probably a stupid question, but I still want to ask Fillmore <fillmore_remove@hotmail.com> - 2016-04-10 22:48 -0400
        Re: Most probably a stupid question, but I still want to ask Steven D'Aprano <steve@pearwood.info> - 2016-04-11 13:54 +1000
          Re: Most probably a stupid question, but I still want to ask Fillmore <fillmore_remove@hotmail.com> - 2016-04-11 00:03 -0400
            Re: Most probably a stupid question, but I still want to ask Stephen Hansen <me+python@ixokai.io> - 2016-04-10 21:46 -0700
              Re: Most probably a stupid question, but I still want to ask Rustom Mody <rustompmody@gmail.com> - 2016-04-10 22:18 -0700
                Re: Most probably a stupid question, but I still want to ask Stephen Hansen <me+python@ixokai.io> - 2016-04-10 22:42 -0700
                  Re: Most probably a stupid question, but I still want to ask Rustom Mody <rustompmody@gmail.com> - 2016-04-10 23:57 -0700
            Re: Most probably a stupid question, but I still want to ask Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-04-11 17:50 +1000

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#106838

funny, but it seems to me that you are taking it personally... thank god i even apologized
in advance for what was most probably a stupid question..

On 04/10/2016 09:50 PM, Steven D'Aprano wrote:
>
> Fillmore, you should feel very pleased with yourself. All the tens of
> thousands of Python programmers, and millions of lines of code written in
> the language, but nobody until now was able to see what you alone had the
> intelligence and clarity of thought to spot. Well done!
>
>
>

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#106847

On Mon, 11 Apr 2016 12:48 pm, Fillmore wrote:

> 
> funny, but it seems to me that you are taking it personally... thank god i
> even apologized in advance for what was most probably a stupid question..

I hope you did get a laugh out of it, because it wasn't meant to be nasty.
But it was meant to get you to think about statements about betraying
principles and other inflammatory remarks.


-- 
Steven

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#106848

On 04/10/2016 11:54 PM, Steven D'Aprano wrote:
> On Mon, 11 Apr 2016 12:48 pm, Fillmore wrote:
>
>>
>> funny, but it seems to me that you are taking it personally... thank god i
>> even apologized in advance for what was most probably a stupid question..
>
> I hope you did get a laugh out of it, because it wasn't meant to be nasty.
> But it was meant to get you to think about statements about betraying
> principles and other inflammatory remarks.

I did have a laugh.

I don't think I talked about betraying principles. I just mentioned that in my newbie
mind, I experienced what I perceived as a discontinuity. My limited understanding of
what builds tuples and the (almost always to be avoided) use of eval() were the origin
of my perplexities.

I'll make sure I approach the temple of pythonistas bare-footed and with greater humility next time

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#106853

On Sun, Apr 10, 2016, at 09:03 PM, Fillmore wrote:
> and the (almost always to be avoided) use of eval()

FWIW, there's ast.literal_eval which is safe and there's no reason to
avoid it. You'll still have to deal with the fact that a single string
on a line will return a string while multiples will return a tuple, but
how you're doing that (checking the type of the result) is fine.

--Stephen
m e @ i x o k a i . i o

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#106857

On Monday, April 11, 2016 at 10:17:13 AM UTC+5:30, Stephen Hansen wrote:
> On Sun, Apr 10, 2016, at 09:03 PM, Fillmore wrote:
> > and the (almost always to be avoided) use of eval()
> 
> FWIW, there's ast.literal_eval which is safe and there's no reason to
> avoid it.

Its error reporting is clunky:

>>> from ast import literal_eval as le
>>> le("(1)")
1
>>> le("(1,)")
(1,)
>>> le("1")
1
>>> le("{1:x}")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/ast.py", line 80, in literal_eval
    return _convert(node_or_string)
  File "/usr/lib/python2.7/ast.py", line 63, in _convert
    in zip(node.keys, node.values))
  File "/usr/lib/python2.7/ast.py", line 62, in <genexpr>
    return dict((_convert(k), _convert(v)) for k, v
  File "/usr/lib/python2.7/ast.py", line 79, in _convert
    raise ValueError('malformed string')
ValueError: malformed string


> You'll still have to deal with the fact that a single string
> on a line will return a string while multiples will return a tuple, but
> how you're doing that (checking the type of the result) is fine.

Yes...
0 and 1 length tuples are special cases even if we argue till we are blue in 
the face

To Fillmore:

Go via lists and the special cases can be obviated:
>>> def br(s): return "[" + s + "]"
>>> s0=""
>>> s1="1"
>>> s2="1,2"
>>> le(br(s0))
[]
>>> le(br(s1))
[1]
>>> le(br(s2))
[1,2]

Then tuplify (if you so wish)
>>> tuple(le(br(s0)))
()
>>> tuple(le(br(s1)))
(1,)
>>> tuple(le(br(s2)))
(1, 2)

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#106861

On Sun, Apr 10, 2016, at 10:18 PM, Rustom Mody wrote:
> On Monday, April 11, 2016 at 10:17:13 AM UTC+5:30, Stephen Hansen wrote:
> > On Sun, Apr 10, 2016, at 09:03 PM, Fillmore wrote:
> > > and the (almost always to be avoided) use of eval()
> > 
> > FWIW, there's ast.literal_eval which is safe and there's no reason to
> > avoid it.
> 
> Its error reporting is clunky:
> 
> >>> from ast import literal_eval as le
> >>> le("(1)")
> 1
> >>> le("(1,)")
> (1,)
> >>> le("1")
> 1
> >>> le("{1:x}")
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "/usr/lib/python2.7/ast.py", line 80, in literal_eval
>     return _convert(node_or_string)
>   File "/usr/lib/python2.7/ast.py", line 63, in _convert
>     in zip(node.keys, node.values))
>   File "/usr/lib/python2.7/ast.py", line 62, in <genexpr>
>     return dict((_convert(k), _convert(v)) for k, v
>   File "/usr/lib/python2.7/ast.py", line 79, in _convert
>     raise ValueError('malformed string')
> ValueError: malformed string

So? Worst case scenario, someone puts invalid data into the file and it
throws an exception. Could it be more specific? Maybe, but I don't see
why it needs to be. If your input isn't reliably formatted, catch
ValueError and log it and fix (either what wrote it or change how you
read it).

--S

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#106863

On Monday, April 11, 2016 at 11:12:39 AM UTC+5:30, Stephen Hansen wrote:
> On Sun, Apr 10, 2016, at 10:18 PM, Rustom Mody wrote:
> > On Monday, April 11, 2016 at 10:17:13 AM UTC+5:30, Stephen Hansen wrote:
> > > On Sun, Apr 10, 2016, at 09:03 PM, Fillmore wrote:
> > > > and the (almost always to be avoided) use of eval()
> > > 
> > > FWIW, there's ast.literal_eval which is safe and there's no reason to
> > > avoid it.
> > 
> > Its error reporting is clunky:
> > 
> > >>> from ast import literal_eval as le
> > >>> le("(1)")
> > 1
> > >>> le("(1,)")
> > (1,)
> > >>> le("1")
> > 1
> > >>> le("{1:x}")
> > Traceback (most recent call last):
> >   File "<stdin>", line 1, in <module>
> >   File "/usr/lib/python2.7/ast.py", line 80, in literal_eval
> >     return _convert(node_or_string)
> >   File "/usr/lib/python2.7/ast.py", line 63, in _convert
> >     in zip(node.keys, node.values))
> >   File "/usr/lib/python2.7/ast.py", line 62, in <genexpr>
> >     return dict((_convert(k), _convert(v)) for k, v
> >   File "/usr/lib/python2.7/ast.py", line 79, in _convert
> >     raise ValueError('malformed string')
> > ValueError: malformed string
> 
> So? Worst case scenario, someone puts invalid data into the file and it
> throws an exception. Could it be more specific? Maybe, but I don't see
> why it needs to be. If your input isn't reliably formatted, catch
> ValueError and log it and fix (either what wrote it or change how you
> read it).

Sorry... Didnt mean "dont use!"
Just "Heres a flipside to consider"
Also that the OP's question is not a classic "Avoid eval like the plague"
but "Many nooks and crannies in the syntax" issue

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#106865

On Monday 11 April 2016 14:03, Fillmore wrote:

> I'll make sure I approach the temple of pythonistas bare-footed and with
> greater humility next time

Don't forget to rip your clothes into rags and heap ashes on your head too.


-- 
Steve

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