pyunitx 0.1.0

First-class manipulation of physical quantities

Units

When doing calculations using physical measurements, it's all too easy to forget to account for units. This can result in problems when you find you've been adding kilograms to newtons and your calculation is off by a factor of ten.

This library uses the standard library decimal.Decimal for all calculations to avoid most floating-point calculation pitfalls. Values given are automatically converted so you can enter any value that constructor can take. Functionally, this means that float notation should be given as strings rather than float literals.

Q. How many meters does light travel in a millisecond?

>>> from pyunitx.time import seconds
>>> from pyunitx.constants import c
>>> 
>>> (c * seconds("1e-3")).sig_figs(5)
2.9979E+5 m

Q. What is that in feet?

>>> from pyunitx.time import seconds
>>> from pyunitx.constants import c
>>> 
>>> (c * seconds("1e-3")).to_feet().sig_figs(5)
9.8357E+5 ft

Q. How fast is someone on the equator moving around the center of the earth?

>>> from pyunitx.time import days
>>> from pyunitx.constants import earth_radius
>>> from math import pi
>>> 
>>> circumference = 2 * pi * earth_radius
>>> (circumference / days(1)).to_meters_per_second().sig_figs(3)
464 m s^-1

Q. What's the mass of air in one of your car tires, if the inner radius is 6 inches, the outer radius is 12.5 inches, the width is 8 inches, and it's filled to 42 psi?

>>> from pyunitx.length import inches
>>> from pyunitx.pressure import psi
>>> from pyunitx.constants import R, air_molar_mass
>>> from pyunitx.temperature import celsius, celsius_to_kelvin_absolute
>>> from math import pi
>>> 
>>> volume = (pi * inches(8) * (inches("12.5") ** 2 - inches(6) ** 2)).to_meters_cubed()
>>> pressure = psi(42).to_pascals()
>>> temperature = celsius_to_kelvin_absolute(celsius(25))
>>> mols = pressure * volume / (R * temperature)
>>> mass = mols * air_molar_mass
>>> mass.to_avoirdupois_pounds_mass().sig_figs(3)
0.369 lbm_A

All constants like R are defined in SI base units so you will need to convert your units, but as you can see, that task is easy.