Equation solver in Python

Given a simple equation such as:

x = y + z

You can get the third variable if you bind the other two (ie: y = x - z and z = x - y). A straightforward way to put this in code:

def solve(args):
    if 'x' not in args:
        return args['y'] + args['z']
    elif 'z' not in args:
        return args['x'] - args['y']
    eli开发者_StackOverflow中文版f 'y' not in args:
        return args['x'] - args['z']
    else:
        raise SomeError  

I obviously can take an equation, parse it and simplify it to achieve the same effect. But I believe in doing so I would be re-inventing the wheel. So where's my ready-made wheel?

---

Consider using Sympy. It includes various tools to solve equations and a lot more.

The following is an excerpt from the docs:

>>> from sympy import I, solve
>>> from sympy.abc import x, y

>>> solve(x**4-1, x)
[1, -1, -I, I]