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sympy expressions in models

Project description


This project aims to explore symbolic modelling with object orientated programming. The heavy lifting is done by the sympy library. This module just provides a class to derive models from.

An example based on examples/

from modello import InstanceDummy, Modello
from sympy import sqrt

class RightAngleTriangle(Modello):
    a = InstanceDummy("a", real=True, positive=True)
    b = InstanceDummy("b", real=True, positive=True)
    c = sqrt(a**2 + b**2)

T = RightAngleTriangle("T", a=3, b=4)
assert T.c == 5
T = RightAngleTriangle("T", b=4, c=5)
assert T.a == 3

The best place to see how this can be used is to look in the examples directory, which still needs padding out.

The functionality is covered by tests in both and doctests+tests in the examples.


Until a pypi release is made, this can be installed using one of:

# using git+pipenv
pipenv install git+

# using git+pip
pip install --user git+

Currently this requires Python 3.6+ but the version requirements can drop a couple of minor versions easily if there is interest. Python 2.7 isn't planned to be supported as the Modello class relies on PEP-3115.


Run the tests and linting with python test. Pushes have the test suite run against them, and will also publish a release if tagged thanks to GitHub Actions. You can reproduce the Actions locally using act.


  • elaborate on tests/examples
  • think about extending the functionality to allow for a more complete system of constraints, use the RightAngleTriangle example as a base
  • work out patterns for labels/names on symbols so they render nicely
  • for mypy, consider getting value from or removing it
  • implement a first attempt at nested models (named, rather than lists, which would be nice)

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