How to process user supplied formulas?

Question

I have a dictionary containing a set of key values available through a web application: I want to process user supplied formulas like: ((value1+value3)/value4)*100

W

Answer 1

After validating both the formula and the numbers value (f.e. via a regexp) you can do something like:

arr = {'num1':4, 'num2':5, 'num3':7}
formula = '(num1+num2)*num3'

for key, val in arr.items():
    formula = formula.replace(key, str(val))

res = eval(formula)
print res