How to interpret a string as code in Python

How to make a function that can interpret a string as a code ?

var1 = 5
var2 = 10
var3 = 7

str = "(var1*var2)+var3"


result = calculate(str) # I need help to write this function

result should output 57

>Solution :

Use result = eval(str) instead of result = calculate(str).

Disclaimer: eval() should be used carefully since it can execute anything passed to it. More details can be found in this article.