Engineering numerical format PEP discussion
in [Python]
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From: Lie Ryan on 27 Apr 2010 06:08 On 04/27/10 10:47, MRAB wrote: > Mark Dickinson wrote: >> On Apr 26, 4:36 am, Keith <keith.braff...(a)gmail.com> wrote: >>> I am considering writing a PEP for the inclusion of an engineering >>> format specifier, and would appreciate input from others. >> >>> [...] >> >>> I am thinking that if we simply added something like %n (for eNgineer) >>> to the list of format specifiers that we could make life easier for >>> engineers: >>> >>> ("%n" % 12345) == "12.345e+03" >>> ("%n" % 1234) == "1.234e+03" >>> ("%n" % 123) == "123e+00" >>> ("%n" % 1.2345e-5) == "12.345e+06" >> >> I don't think there's much chance of getting changes to old-style >> string formatting accepted; you might be better off aiming at the new- >> style string formatting. (And there, the 'n' modifier is already >> taken for internationalization, so you'd have to find something >> different. :) >> > "e" is already used, "n" is already used, "g" is already used, etc > > "t" for "powers of a thousand", perhaps? (Or "m"?) or perhaps as an extension to 'e', activated by '3e' (but that's occupied for adding spaces, need to think of another way...)
From: Gregory Ewing on 27 Apr 2010 06:52 Keith wrote: > I kinda like "m" for the whole Greco- > Roman angle, now that you point it out :-) I like "m", too. -- Greg
From: Mark Dickinson on 27 Apr 2010 09:03 On Apr 27, 2:16 am, Keith <keith.braff...(a)gmail.com> wrote: > On Apr 26, 8:47 pm, MRAB <pyt...(a)mrabarnett.plus.com> wrote: > > > "t" for "powers of a thousand", perhaps? (Or "m"?) > > Both of those letters are fine. I kinda like "m" for the whole Greco- > Roman angle, now that you point it out :-) By the way, there's already a feature request open for this: http://bugs.python.org/issue8060 That might be a good place to hash out the precise semantics. If you could provide unit tests and/or an implementation that would likely help move the issue along. Mark
From: cassiope on 27 Apr 2010 11:24 On Apr 25, 10:19 pm, Chris Rebert <c...(a)rebertia.com> wrote: > On Sun, Apr 25, 2010 at 9:42 PM, Keith <keith.braff...(a)gmail.com> wrote: > > On Apr 26, 12:02 am, Chris Rebert <c...(a)rebertia.com> wrote: > >> On Sun, Apr 25, 2010 at 8:36 PM, Keith <keith.braff...(a)gmail.com> wrote: > >> > I am considering writing a PEP for the inclusion of an engineering > >> > format specifier, and would appreciate input from others. > > snip > >> Relevant related information: > >> The Decimal datatype supports engineering format directly:http://docs.python.org/library/decimal.html#decimal.Decimal.to_eng_st... > > > Thanks for pointing that out. Does the engineering community get by > > with the decimal module? > > > Even though this uses the to_eng_string() function, and even though I > > am using the decimal.Context class: > > >>>> c = decimal.Context(prec=5) > >>>> decimal.Decimal(1234567).to_eng_string(c) > > '1234567' > > > That is not an engineering notation string. > > Apparently either you and the General Decimal Arithmetic spec differ > on what constitutes engineering notation, there's a bug in the Python > decimal library, or you're hitting some obscure part of the spec's > definition. I don't have the expertise to know which is the case. > > The spec:http://speleotrove.com/decimal/decarith.pdf > (to-engineering-string is on page 20 if you're interested) > > Cheers, > Chris > --http://blog.rebertia.com As has been pointed out, the Decimal implementation may not have all the features desired (i.e. forcing a particular "exponent", or a particular number of significant digits). Perhaps it could be enhanced. The other concern is computational complexity - having to perform complex engineering calculations in Decimal form is presumably more burdensome than in floats. What I've done for years is to have a function that converts an arbitrary float into a string. The function has an optional parameter that specifies the number of digits of the output. Isn't as "automatic", of course, probably showing its C origins. -f
From: Keith on 27 Apr 2010 13:09
On Apr 27, 9:03 am, Mark Dickinson <dicki...(a)gmail.com> wrote: > On Apr 27, 2:16 am, Keith <keith.braff...(a)gmail.com> wrote: > > > On Apr 26, 8:47 pm, MRAB <pyt...(a)mrabarnett.plus.com> wrote: > > > > "t" for "powers of a thousand", perhaps? (Or "m"?) > > > Both of those letters are fine. I kinda like "m" for the whole Greco- > > Roman angle, now that you point it out :-) > > By the way, there's already a feature request open for this: > > http://bugs.python.org/issue8060 > > That might be a good place to hash out the precise semantics. If you > could provide unit tests and/or an implementation that would likely > help move the issue along. > > Mark Oh nice! I don't know how I missed that. --Keith Brafford |