On 5 May 2016 at 08:28, Paul Moore <p.f.mo...@gmail.com> wrote: > On 4 May 2016 at 23:11, Chris Barker <chris.bar...@noaa.gov> wrote: >> so it could be purely declarative, but users could also put code in there to >> customize the configuration on the fly, too. > > That basically repeats the mistake that was made with setup.py. We > explicitly don't want an executable format for specifying build > configuration.
This configuration vs customisation distinction is probably worth spelling out for folks without a formal software engineering or computer science background, so: Customisation is programming: you're writing plugins in a Turing complete language (where "Turing complete" is a computer science classification that says "any program that can be expressed at all, can be expressed in this language", although it doesn't make any promises about readability). As such, Python "config files" like setup.py in distutils and settings.py in Django are actually software *customisation* interfaces - the only way to reliably interact with them is to run them and see what happens. Anything you do via static analysis rather than code execution is a *heuristic* that may fail on some code that "works" when executed. Configuration is different: you're choosing amongst a set of possibilities that have been constrained in some way, and those constraints are structurally enforced. Usually that enforcement is handled by making the configuration declarative - it's in some passive format like an ini file or JSON, and if it gets too repetitive then you introduce a config generator, rather than making the format itself more sophisticated. The big advantage of configuration over customisation is that you substantially increase the degrees of freedom in how *consumers* of that configuration are implemented - no longer do you need a full Python runtime (or whatever), you just need an ini file parser, or a JSON decoder, and then you can look at just the bits you care about for your particular use case and ignore the rest. Regards, Nick. P.S. Fun fact: XML (as formally specified) is a customisation language, rather than a configuration language. If you want to safely use it as a configuration language, you need to use a library like defusedxml to cut it down to a non-Turing complete subset of the spec. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Distutils-SIG maillist - Distutils-SIG@python.org https://mail.python.org/mailman/listinfo/distutils-sig
