Your task is to create a function that does four basic mathematical operations.
The function should take three arguments - operation(string/char), value1(number), value2(number).
The function should return result of numbers after applying the chosen operation.
Examples
basic_op('+', 4, 7) # Output: 11
basic_op('-', 15, 18) # Output: -3
basic_op('*', 5, 5) # Output: 25
basic_op('/', 49, 7) # Output: 7