Safe way to parse user-supplied mathematical formula in Python

Question

Is there a math expressions parser + evaluator for Python?

I am not the first to ask this question, but answers usually point to eval(). For instance,

Answer 1

I'd suggest using ast.parse and then whitelisting the parse tree.

tree = ast.parse(s, mode='eval')
valid = all(isinstance(node, whitelist) for node in ast.walk(tree))
if valid:
    result = eval(compile(tree, filename='', mode='eval'),
                  {"__builtins__": None}, safe_dict)

Here whitelist could be something like:

whitelist = (ast.Expression, ast.Call, ast.Name, ast.Load,
             ast.BinOp, ast.UnaryOp, ast.operator, ast.unaryop, ast.cmpop,
             ast.Num,
            )