On 30 August 2016 at 13:48, Ken Kundert <python-id...@shalmirane.com> wrote: > >>> d_sun = 93e6*u.imperial.mile > >>> print(d_sun.to(u.parsec)) > 4.850441695494146e-06 pc
The "imperial.mile" example here highlights one key benefit that expression based approaches enjoy over dedicated syntax: easy access to Python's existing namespace features. As a quick implementation sketch, consider something like: >>> si_scaling = dict(k=1000, m=0.001) >>> class SIScale: ... def __getattr__(self, key): ... return SIUnit(si_scaling[key]) ... >>> class SIUnit: ... def __init__(self, value): ... self.value = value ... def __getattr__(self, ignored): ... return self.value ... >>> si = SIScale() >>> 500 * si.k.m 500000 >>> 500 * si.k.parsec 500000 >>> 500 * si.m.m 0.5 >>> 500 * si.m.N 0.5 You could also relatively easily adapt that such that there there was only one level of lookup, and you could write the examples without the second dot (you'd just need to do some parsing of the key value in __getattr__ to separate the SI prefix from the nominal units) One particular benefit of this kind of approach is that you automatically avoid the "E" ambiguity problem, since there's nothing wrong with "si.E" from Python's perspective. You also gain an easy hook to attach interactive help: "help(si)" (or si? in IPython terms) Expanding out to full dimensional analysis with something like astropy.units also becomes relatively straightforward, just by changing the kind of value that __getattr__ returns. Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
