phyunit 0.2.0

A package for physical units.

PhyUnit

PhyUnit is a Python package for physical units and quantities.

Installation

PhyUnit has been uploaded as a package in pypi: phyunit. You can directly install it using pip.

pip install phyunit

Quickstart: sub-package phyunit.SI

Sub-package phyunit.SI implements SI unit definitions, from which you can import many very useful classes:

class	content
phyunit.SI.SI	physical constants in SI unit
phyunit.SI.si	SI units
phyunit.SI.prefix	SI unit prefixes
phyunit.SI.particle	constants in particle physics
phyunit.SI.conversion.au	atomic unit value in SI
phyunit.SI.conversion.nu	natural unit value in SI
phyunit.SI.conversion.Planck	Planck unit value in SI

>>> from phyunit.SI import SI, si

SI: SI physical constant class

class SI provide physical constants defined by (or derived from) SI unit system.

Like speed of light c, Planck constant h, electron mass me... directly use them.

>>> from phyunit.SI import SI

>>> SI.c
Constant(299792458, m/s)

>>> print(SI.me)
9.1093837139e-31 kg

>>> print(SI.me * SI.c**2)
8.18710578796845e-14 kg·m²/s²

particle class contains constants in particle physics, it is separated from SI class for symbol and namespace clarity.

>>> from phyunit.SI import particle

>>> print(particle.mtau)
3.16754e-27 kg

si: SI unit class

class si provides common SI units, like meter m, second s, and units with prefix like centimeter cm.

>>> from phyunit.SI import si

>>> print(1 * si.m / si.s)
1 m/s

>>> print((760 * si.mmHg).to(si.Pa))
101325.0 Pa

prefix: unit prefix factor

class prefix contains prefix from quetta- (Q-, = 10^30) to quecto- (q-, = 10^-30), and byte prefix like ki- (2^10 = 1024), Mi- (2^20), Gi- (2^30)... It's just a number factor, not Quantity.

>>> from phyunit.SI import prefix

>>> prefix.mega
1000000.0

>>> prefix.Pi  # 2**50
1125899906842624

conversion module: au, nu and Planck

Convert values in other unit system to SI unit, i.e. au.length is the atomic unit (a.u.) of length in SI unit.

>>> from phyunit.SI.conversion import au

>>> print(1 * au.length)  # 1 Bohr radius
5.291772105437146e-11 m

Tutorial: Define phyunit.Quantity

Import class phyunit.Quantity to define a quantity object with a certain value and unit:

>>> from phyunit import Quantity

>>> F = Quantity(1, 'kg.m/s2')

where F is a Quantity object, and it has properties:

>>> F.value
1

>>> F.unit
Unit('kg·m/s²')

>>> F.dimension
Dimension(T=-2, L=1, M=1, I=0, Theta=0, N=0, J=0)

Using with numpy

phyunit is compatible with numpy. You can directly operate on numpy.ndarray with units.

>>> import numpy as np

>>> length = np.array([1, 2, 3]) * si.m
>>> print(length)
[1 2 3] m

>>> print(length**2)
[1 4 9] m²

>>> print(np.sum(lengths))
6 m

Example

phyunit is also compatible with matplotlib.

Note that phyunit.Quantity as a parameter in pyplot.plot() is actually its value property.

import numpy as np
from matplotlib import pyplot as plt
from phyunit.SI import SI, si

lam = np.linspace(0.01, 5, 100)[:, None] * si.um  # wavelength
T = np.array([3000, 4000, 5000])[None, :] * si.K  # temperature

nu = SI.c / lam  # frequency
I = 2 * SI.h * SI.c**2 / (lam**5 * (np.exp(SI.h * nu / (SI.kB * T)) - 1))  # intensity

plt.plot(lam, I)  # same as `plt.plot(lam.value, I.value)`
plt.xlabel('Wavelength [um]')
plt.ylabel('Intensity [W/m^3/sr]')
plt.title('Blackbody Radiation')
plt.show()