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
```python
basic_op('+', 4, 7)         # Output: 11
basic_op('-', 15, 18)       # Output: -3
basic_op('*', 5, 5)         # Output: 25
basic_op('/', 49, 7)        # Output: 7
```
def basic_op(operator, value1, value2):
    if operator == '+':
        result = value1 + value2
    elif operator == '-':
        result = value1 - value2
    elif operator == '*':
        result = value1 * value2
    elif operator == '/':
        result = value1 / value2
    else:
        result = None
    return result
    

def basic_op(operator, value1, value2):
    if operator == '+':
        result = value1 + value2
    elif operator == '-':
        result = value1 - value2
    elif operator == '*':
        result = value1 * value2
    elif operator == '/':
        result = value1 / value2
    else:
        result = None
    return result
    
