nist

From the National Institute of Standards and Technology’s Office OF Weights and Measures, one can find a handy list of all the metric prefixes: e.g.

| Purpose | Name | Symbol | Factor | Name | |----------------------------------|----------------------------|--------|--------------|--------------| | larger quantities or whole units | quetta | Q | $$10^{30}$$ | nonillion | | | ronna | R | $$10^{27}$$ | octillion | | | yotta | Y | $$10^{24}$$ | septillion | | | … | … | … | … | | | hecto Example: hectare | h | $$10^{2}$$ | hundred | | | deka Example: dekameter | da | $$10^{1}$$ | ten | | | | | $$10^{o}$$ | one | | | deci Example: decimeter | da | $$10^{-1}$$ | tenth | | | centi Example: centigram | h | $$10^{-2}$$ | hundredth | | | … | … | … | … | | | yocto Example: yoctosecond | y | $$10^{-24}$$ | septillionth | | | ronto | r | $$10^{-27}$$ | octillionth | | smaller quantities or sub units | quecto | q | $$10^{-30}$$ | nonillionth |

Oh how nice it would be to have a class like unit which we could subclass and use as follows:

class second(unit): 
    name = 'second'

s1 = second(1)
s1, s1.kilo, s1.milli, s1.to(3), float(s1.to(3))
(1.0 S, 0.001 KS, 1000.0 mS, 0.001 KS, 0.001)

ah so easy to convert between and even have clean formatting.

Install

pip install nist

Usage

`fact`

While each fact (factor) has base: ClassVar[int] = 10, base is actually an instance variable.

>>> float(kilo()), float(kilo(base=2)), float(kilo(base=5)), float(kilo(base=10))

(1000.0, 8.0, 125.0, 1000.0)

In case that behavior is not obvious fact is really just a named and explicilty signed exponent:

>>> kb = kilo(base=2)
>>> kb.abrv, kb.base, kb.expo, kb.sign, kb.ekey, float(kb)

('kilo', 2, 3, 1, 3, 8.0)

Each fact uses efmt for its representation by default efmt is True, but can be turned off by setting efmt to False.

>>> (
    (decka(), hecto(), kilo(), mega(), giga(), tera()),
    (decka(showefmt=False), hecto(showefmt=False), kilo(showefmt=False), mega(showefmt=False), giga(showefmt=False), tera(showefmt=False))
)

((e+1, e+2, e+3, e+6, e+9, e+12), (F1P, F2P, F3P, F6P, F9P, F12P))

Actually we have three formats to work with:

>>> kilo().fstr, kilo(showbase=True).bstr, kilo(showbase=True).efmt

('F3P', '10^+3', 'e+3')

`unit`

The goal of the unit class is to make it easy to create units:

class second(unit): 
    name = 'second'

>>> s1 = second(1)
>>> s1, s1.kilo, s1.milli, s1.to(3), float(s1.to(3)), s1.shownumb


(1.0 S, 0.001 KS, 1000.0 mS, 0.001 KS, 0.001, True)

We can also explore all the different ways of viewing formats:

import pandas as pd

results = list()
factors = (tera, decka, deci, centi, milli, pico)
for fcls in factors:
    for flt in (1, 20, 0.03):
        for factrepr in {'abrv', 'name', 'symb'}:
            for shownumb in (True, False):
                for abrvunit in (True, False):
                    res = fmtunit(
                        org = flt, flt=flt / float(fcls()), unt = unit, fct = fcls,
                        factrepr=factrepr, shownumb=shownumb, abrvunit=abrvunit,
                        unitname='second', factname=None, ndig=3
                    )

                    results.append(dict(
                        fname=fcls.name, flt=flt, res=res, org = flt / float(fcls()),
                        shownumb=shownumb, abrvunit=abrvunit, factrepr=factrepr
                    ))

df = pd.DataFrame(results).sort_values(by=['fname', 'res'])
df.head()

| | fname | flt | res | org | shownumb | abrvunit | factrepr | |----:|:----------|-----:|:-------------|----:|:---------|:---------|:---------| | 134 | hundredth | 0.03 | 0.03 S | 3 | False | True | name | | 138 | hundredth | 0.03 | 0.03 S | 3 | False | True | abrv | | 142 | hundredth | 0.03 | 0.03 S | 3 | False | True | symb | | 143 | hundredth | 0.03 | 0.03 S | 3 | False | False | symb | | 135 | hundredth | 0.03 | 0.03 seconds | 3 | False | False | name |