Equation parsing in Python

How can I (easily) take a string such as "sin(x)*x^2" which might be entered by a user at runtime and produce a Python function that could be evaluated for any value of x?

Solution 1:

Python's own internal compiler can parse this, if you use Python notation.

If your change the notation slightly, you'll be happier.

import compiler
eq= "sin(x)*x**2"
ast= compiler.parse( eq )

You get an abstract syntax tree that you can work with.

Solution 2:

You can use Python parser:

import parser
from math import sin

formula = "sin(x)*x**2"
code = parser.expr(formula).compile()
x = 10
print(eval(code))

It performs better than pure eval and, of course, avoids code injection!