On Thu, Aug 25, 2016 at 2:28 PM, Ken Kundert <python-id...@shalmirane.com> wrote: > I propose that support for SI scale factors be added to Python. This would > be very helpful for any program that heavily uses real numbers, such as those > involved with scientific and engineering computation. There would be two > primary > changes. First, the lexer would be enhanced to take real literals with the > following forms: > > c1 = 1nF (same as: c1 = 1e-9 # F ) > c = 299.79M (same as: c = 299.79e6 ) > f_hy = 1.4204GHz (same as: f_hy = 1.4204e9 # Hz) > > Basically a scale factor and units may follow a number, both of which are > optional, but if the units are given the scale factor must also be given. Any > units given could be kept with the number and would be accessible through an > attribute or method call, or if it is felt that the cost of storing the units > are too high, it may simply be discarded, in which case it is simply serving > as > documentation.
If units are retained, what you have is no longer a simple number, but a value with a unit, and is a quite different beast. (For instance, addition would have to cope with unit mismatches (probably by throwing an error), and multiplication would have to combine the units (length * length = area).) That would be a huge new feature. I'd be inclined to require, for simplicity, that the scale factor and the unit be separated with a hash: c1 = 1n#F c = 299.79M f_hy = 1.4204G#Hz It reads almost as well as "GHz" does, but is clearly non-semantic. The resulting values would simply be floats, and the actual tag would be discarded - there'd be no difference between 1.4204G and 1420.4M, and the %q formatting code would render them the same way. Question, though: What happens with exa-? Currently, if the parser sees "1E", it'll expect to see another number, eg 1E+1 == 10.0. Will this double meaning cause confusion? ChrisA _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
