phyunit 0.1.3

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 2 very useful classes:

class	content
phyunit.SI.SI	SI physical constant
phyunit.SI.si	SI unit
phyunit.SI.prefix	SI unit prefix

>>> 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

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

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()