You are required to create a simple calculator that returns the result of addition, subtraction, multiplication or division of two numbers.
Your function will accept three arguments:
The first and second argument should be numbers.
The third argument should represent a sign indicating the operation to perform on these two numbers.
```if-not:csharp
if the variables are not numbers or the sign does not belong to the list above a message "unknown value" must be returned.
```
```if:csharp
If the sign is not a valid sign, throw an ArgumentException.
```
# Example:
```python
calculator(1, 2, '+') => 3
calculator(1, 2, '$') # result will be "unknown value"
```
Good luck!
def calculator(x,y,op):
    if type(x) != int or type(y) != int:
        return('unknown value')
    elif op == '/':
        return(x/y)
    elif op == '*':
        return(x*y)
    elif op == '-':
        return(x-y)
    elif op == '+':
        return(x+y)
    else:
        return('unknown value')
    pass
def calculator(x,y,op):
    if type(x) != int or type(y) != int:
        return('unknown value')
    elif op == '/':
        return(x/y)
    elif op == '*':
        return(x*y)
    elif op == '-':
        return(x-y)
    elif op == '+':
        return(x+y)
    else:
        return('unknown value')
    pass