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Manipulate physical quantities in Python

Project description


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


pip install physipy


  • 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.

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) :

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.


Here are some functionnality/fixes/TODOs for down the road :

  • Add a list of main functionnalities of the package
  • Improve the README
  • Create a full benchmark based on an expected behaviour, and bench physical quantities packages.
  • Improve numpy compatibility
  • Add uncertainty support
  • Allow changing base unit system (cgs, Planck units, etc)


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


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

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