MathJSON Solver

MathJSON Solver is a Python module to numerically evaluate MathJSON expressions, like ["Add", 1, 2]. It is developed by Longenesis to enable numerical evaluation of user provided mathematical expressions in Longenesis digital health products. Its development was inspired by CortexJS Compute Engine.

Please ask questions and share feedback in our Gitter chat https://gitter.im/mathjson-solver/community.

How to use

from mathjson_solver import create_solver

parameters = {"x": 2, "y": 3}
expression = ["Add", "x", "y", 4]

solver = create_solver(parameters)
answer = solver(expression)

print(answer)
# 9, because 2+3+4=9

Currently supported constructs

Find the full list of supported constructs in the docs/README.md.

Exception handling

A MathJSONException is raised when expression cannot be evaluated. Import MathJSONException to handle it:

from mathjson_solver import create_solver, MathJSONException

solver = create_solver({})
try:
    solver(["Divide", 1, 0])
except MathJSONException:
    pass
    # invoke your own exception logger here

Left unhandled, the exception will look like MathJSONException("Problem in Divide. ['Divide', 1, 0]. division by zero").

Strict mode

By default, a parameter that is not defined evaluates to its own name, as a string, and each operator handles that string its own way (comparisons return False, Add skips it). Use create_solver(parameters, strict=True) to raise instead:

from mathjson_solver import create_solver, MathJSONException

solver = create_solver({"a": 0.7, "b": None}, strict=True)
solver(["Greater", "c", 0.6])  # MathJSONException: Parameter 'c' is not defined
solver(["Add", "a", "b"])      # MathJSONException: Parameter 'b' is None

The exception's e is a MathJSONUnresolvedParameter (a KeyError), and its expr / construct are the innermost expression containing the parameter.

In strict mode:

• a parameter whose value is None is unresolved too;
• string values of parameters are returned as is, not resolved again as names;
• string literals must be written with Str: ["Str", "plasma"] returns "plasma" without looking it up. Bare strings anywhere else (Switch cases, In arrays, Strptime formats, ...) are parameter names;
• If, Map and HasMatchingSublist still catch a MathJSONException raised by a branch or an element, as they do in the default mode.

How to run tests

Make sure you have pytest installed. Then cd into project directory and run:

pytest