如何从 python 中的字符串中提取数学方程式？

Question

I have a problem with math equation and string. If a user gives a math equation in string format how do I get that out of string and calculate values?

Input: 
x = 1
y = 2
formula = "x+y"
Output:
formula = x+y
formula = 3

Answer 1

>>> x, y = 1, 2
>>> formula = "x+y"
>>> print('formula = ' + formula)
formula = x+y
>>> print('formula = ' + str(eval(formula)))
formula = 3