chenmich/physipy

physipy

This python package allows you to manipulate physical quantities, basically considering in the association of a value (scalar, numpy.ndarray and more) and a physical unit (like meter or joule).

>>> from physipy.quickstart import nm, hp, c, J
>>> E_ph = hp * c / (500 * nm)
>>> print(E_ph)
3.9728916483435158e-19 kg*m**2/s**2
>>> E_ph.favunit = J
>>> print(E_ph)
3.9728916483435158e-19 J

For a quickstart, check the quickstart notebook on the homepage Get a live session at

Installation

pip install physipy

Goals

• Few LOC
• Simple architecture, with only 2 classes (namely Dimension and Quantity)
• High numpy compatibility
• Human-readable syntax (fast syntax !)

Use case

• Define scalar and arrays of physical quantities
• Compute operation between them : add, sub, mul, div, pow, and so on
• Display physical quantities in various “units”

Implementation approach

The implementation is pretty simple :

• a Dimension object represents a physical dimension. For now, these dimension are based on the SI unit. It is basically a dictionary where the keys represent the base dimensions, and the values are the exponent these dimensions.
• a Quantity object is simply the association of a value, scalar or array (or more!), and a Dimension object. Note that this Quantity classe does not sub-class numpy.ndarray (although Quantity objects are compatible with numpy's ufuncs). Most of the work is done by this class.
• By default, a Quantity is displayed in term of SI untis. To express a Quantity in another unit, just set the "favunit", which stands for "favourite unit" of the Quantity : my_toe_length.favunit = mm.
• Plenty of common units (ex : Watt) and constants (ex : speed of light) are packed in. Your physical quantities (my_toe_length), units (kg), and constants (kB) are all Quantity objects.

Numpy's support

See NEP35.

Known issues

numpy.full

import numpy as np
from physipy import m
np.full((3,3), 2*m)

About angles and units

See : https://www.bipm.org/en/CGPM/db/20/8/. Astropy's base units : https://docs.astropy.org/en/stable/units/standard_units.html#enabling-other-units

Alternative packages

There are plenty of python packages that handle physical quantities computation. Some of them are full packages while some are just plain python module. Here is a list of those I could find (approximately sorted by guessed-popularity) :

• astropy
• sympy
• pint
• forallpeople
• unyt
• python-measurement
• Unum
• scipp
• magnitude
• physics.py : there are actually several packages based on the same core code : ipython-physics (python 2 only) and python3-physics (python 3 only)
• ScientificPython.Scientific.Physics.PhysicalQuantities
• numericalunits
• dimensions.py (python 2 only)
• buckingham
• units
• quantities
• physical-quantities
• brian
• quantiphy
• parampy
• pynbody
• python-units
• misu
• and finally pysics from which this package was inspired

If you know another package that is not in this list yet, feel free to contribute ! Also, if you are interested in the subject of physical quantities packages in python, check this quantities-comparison repo and this talk. Also check this comparison table.

License

This project is licensed under the MIT License - see the LICENSE.md file for details

Acknowledgment

Thumbs up to phicem and his pysics package, on which this package was highly inspired. Check it out !