[Distutils] Are chained comparisons allowed in environment markers?

[Nick Coghlan]

On Sun, Apr 28, 2013 at 12:47 AM, PJ Eby <pje at telecommunity.com> wrote:
> On Sat, Apr 27, 2013 at 5:46 AM, Vinay Sajip <vinay_sajip at yahoo.co.uk> wrote:
>> At the moment, distlib
>> allows expressions like "python_version >= '2.6'" or "python_version < '3.5'"
>> which are also not mentioned in the PEP. I don't recall seeing any discussion
>> around why allowing inequalities might be a bad idea, but perhaps someone
>> can point me to it? Perhaps it should be mentioned in the PEP.
>
> I don't know of any reasons myself.  Perhaps it was thought that
> restricting the syntax would make it easier to implement?  For Python,
> that's not especially true.

I don't know for sure either - I pretty much inherited it as is from
PEP 345, and otherwise haven't messed with it. I already have a note
in the next draft saying that we might want access to the version
specifier comparisons to make it easier to place constraints on the
Python version.

> The marker syntax has some other annoying quirks that make it more
> difficult to implement and weird to spell, anyway, like mixing actual
> things ('sys.platform') with non-real things (e.g. 'platform.machine'
> that's really 'platform.machine()').  It would make a lot more sense
> (and simplify implementations) to just say 'platform_machine' or even
> 'machine' in the first place.
>
> OTOH, I hope that we can finalize at least the environment marker
> syntax pronto, so I don't end up with a dead-end version of the
> syntax.

I have my hands full with other aspects of the PEP 426 update, but if
you and Vinay want to thrash out a modified version of the environment
marker syntax (such as always using underscores for names which don't
correspond directly to usable Python expressions), I'd certainly be
willing to consider it. It's pretty decoupled from the rest of the
PEP, which just says in a couple of places "environment marker strings
can go here", and then defines the syntax for them once.

Cheers,
Nick.

--
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia