<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Aug 29, 2016, at 06:08, Erik Bray <<a href="mailto:erik.m.bray@gmail.com" class="">erik.m.bray@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">On Mon, Aug 29, 2016 at 3:05 PM, Erik Bray <</span><a href="mailto:erik.m.bray@gmail.com" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">erik.m.bray@gmail.com</a><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">> wrote:</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">On Mon, Aug 29, 2016 at 9:07 AM, Ken Kundert<br class=""><<a href="mailto:python-ideas@shalmirane.com" class="">python-ideas@shalmirane.com</a>> wrote:<br class=""><blockquote type="cite" class="">On Mon, Aug 29, 2016 at 01:45:20PM +1000, Steven D'Aprano wrote:<br class=""><blockquote type="cite" class="">On Sun, Aug 28, 2016 at 08:26:38PM -0700, Brendan Barnwell wrote:<br class=""><blockquote type="cite" class="">On 2016-08-28 18:44, Ken Kundert wrote:<br class=""><blockquote type="cite" class="">When working with a general purpose programming language, the above numbers<br class="">become:<br class=""><br class=""> 780kpc -> 7.8e+05<br class=""></blockquote></blockquote>[...]<br class=""><br class="">For the record, I don't know what kpc might mean. "kilo pico speed of<br class="">light"? So I looked it up using units, and it is kilo-parsecs. That<br class="">demonstrates that unless your audience is intimately familiar with the<br class="">domain you are working with, adding units (especially units that aren't<br class="">actually used for anything) adds confusion.<br class=""><br class="">Python is not a specialist application targetted at a single domain. It<br class="">is a general purpose programming language where you can expect a lot of<br class="">cross-domain people (e.g. a system administrator asked to hack on a<br class="">script in a domain they know nothing about).<br class=""></blockquote><br class="">I talked to astrophysicist about your comments, and what she said was:<br class="">1. She would love it if Python had built in support for real numbers with SI<br class=""> scale factors<br class="">2. I told her about my library for reading and writing numbers with SI scale<br class=""> factors, and she was much less enthusiastic because using it would require<br class=""> convincing the rest of the group, which would be too much effort.<br class="">3. She was amused by the "kilo pico speed of light" comment, but she was adamant<br class=""> that the fact that you, or some system administrator, does not understand<br class=""> what kpc means has absolutely no affect on her desired to use SI scale<br class=""> factors. Her comment: I did not write it for him.<br class="">4. She pointed out that the software she writes and uses is intended either for<br class=""> herself of other astrophysicists. No system administrators involved.<br class=""></blockquote><br class="">Astropy also has a very powerful units package--originally derived<br class="">from pyunit I think but long since diverged and grown:<br class=""><br class=""><a href="http://docs.astropy.org/en/stable/units/index.html" class="">http://docs.astropy.org/en/stable/units/index.html</a><br class=""><br class="">It was originally developed especially for astronomy/astrophysics use<br class="">and has some pre-defined units that many other packages don't have, as<br class="">well as support for logarithmic units like decibel and optional (and<br class="">customizeable) unit equivalences (e.g. frequency/wavelength or<br class="">flux/power).<br class=""><br class="">That said, its power extends beyond astronomy and I heard through last<br class="">week's EuroScipy that even some biology people have been using it.<br class="">There's been some (informal) talk about splitting it out from Astropy<br class="">into a stand-alone package. This is tricky since almost everything in<br class="">Astropy has been built around it (dimensional calculations are always<br class="">used where possible), but not impossible.<br class=""><br class="">One of the other big advantages of astropy.units is the Quantity class<br class="">representing scale+dimension values. This is deeply integrated into<br class="">Numpy so that units can be attached to Numpy arrays, and all Numpy<br class="">ufuncs can operate on them in a dimensionally meaningful way. The<br class="">needs for this have driven a number of recent features in Numpy. This<br class="">is work that, unfortunately, could never be integrated into the Python<br class="">stdlib.<br class=""></blockquote><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">I'll also add that syntactic support for units has rarely been an</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">issue in Astropy. The existing algebraic rules for units work fine</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">with Python's existing order of operations. It can be *nice* to be</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">able to write "1m" instead of "1 * m" but ultimately it doesn't add</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">much for clarity (and if really desired could be handled with a</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">preparser--something I've considered adding for Astropy sources (via</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">codecs).</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""></div></blockquote><div><br class=""></div><div>I just want to add, as an astrophysicist who uses astropy.units: the astropy solution is pretty great, and I don’t mind the library overhead. I’d much rather have astropy.units, which does dimensional analysis, as well as handling SI prefixes for 2 reasons:</div><div>1. I don’t normally see or use SI prefixes without units, so bare SI prefixes are fairly worthless to me as a scientist. IF the units are going to be there, I’d much rather have a library that does a good job at dimensional analysis, and has taken my domain-specific concerns into account, for reasons fairly well covered in this thread.</div><div>2. I don’t find it cumbersome at all to use something like astropy.units which provides both the prefix and units for my code on input and output. The added syntactic weight of a single import, plus multiplication, is really not that big a burden, and makes it both clear what I am trying to write, and easy for the library to maintain this meaning when I use the variable later. e.g.</div><div>from astropy.units import *</div><div>distance = 10 * km</div><div><br class=""></div><div>If that multiplication symbol is really too much to handle, then I’d rather see python support implicit multiplication as suggested above (i.e. “10 km” is parsed as “10 * km") and domain-specific libraries can support SI prefixes and units.</div><div><br class=""></div><div>~ Alex</div><div><br class=""></div><blockquote type="cite" class=""><div class=""><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">Best,</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">Erik</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">_______________________________________________</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; 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font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">Code of Conduct:<span class="Apple-converted-space"> </span></span><a href="http://python.org/psf/codeofconduct/" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">http://python.org/psf/codeofconduct/</a></div></blockquote></div><br class=""></body></html>