Manipulate physical quantities in Python
Project description
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
- Unum
- 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 !
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