[Distutils] Are chained comparisons allowed in environment markers?

[Daniel Holth]

How do you feel about parenthesis?

It's probably not that hard to prohibit chained comparisons. Do we need an
abnf?

What's wrong with eval?
On Apr 27, 2013 1:42 PM, "PJ Eby" <pje at telecommunity.com> wrote:

> On Sat, Apr 27, 2013 at 11:57 AM, Vinay Sajip <vinay_sajip at yahoo.co.uk>
> wrote:
> > Daniel Holth <dholth <at> gmail.com> writes:
> >
> >> Surely getting farther away from python by trying to prohibit useless
> >> makers just makes the implementation needlessly complex.
> >
> > I'm not quite sure what you mean by "useless" markers. For example,
> distlib
> > checks for e.g. "'2' == '2'" and e.g. "'os.name' == 'os.name'" as these
> are
> > pointless to include in an environment marker, but that's only on the
> basis
> > that (probable) errors shouldn't pass silently.
>
> My test suite actually contains checks like that in order to verify
> and/or logic, i.e., a bunch of "'x'=='x' and 'x'=='y'" type stuff, to
> ensure that operator precedence is handled correctly, so I wouldn't
> want to prohibit those in the spec.
>
> I'm definitely in favor of switching to '_'; it'd let me delete some
> lines from my implementation as well as making things clearer, and on
> top of that it restores compatibility with the PEP 390 marker syntax.
> (For whatever good that is, given that it's apparently being rejected
> soon.  ;-) )
>
> Anyway, I propose keeping the current spec but explicitly
> *prohibiting* chained comparisons and concatenated string constants
> (e.g. 'os.name=="win" "32"', which is valid Python 2 code.)  I would
> also happily prohibit the use of '\' in strings, as that would let me
> get rid of an eval in my implementation.  ;-)
>
> Hm.  Actually i can get rid of that eval already if I use an
> appropriate codec to decode the string...  but that brings up another
> important question: are environment markers Unicode on Python 2?  Do
> we need to support any non-ASCII characters in any of the provided
> variables?  What happens if someone uses an r'', u'', or b'' string
> constant?
>
> I think we need to be a bit pickier about what subset of Python we're
> supporting, so that we don't end up with implementation-defined
> behavior.  Ideally, this would include dumbing strings down to ASCII
> without backslashes or prefix characters.  If in the future a
> non-ASCII usecase occurs for these strings, we could loosen the spec
> then. (Hopefully after setuptools is out of the picture, since it's
> still stuck using 8-bit files with unspecified encodings.  ;-) )
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