Solve in Python:
Given two numbers and an arithmetic operator (the name of it, as a string), return the result of the two numbers having that operator used on them. 

```a``` and ```b``` will both be positive integers, and ```a``` will always be the first number in the operation, and ```b``` always the second.

The four operators are "add", "subtract", "divide", "multiply". 

A few examples: 

``` javascript
ArithmeticFunction.arithmetic(5, 2, "add")      => returns 7
ArithmeticFunction.arithmetic(5, 2, "subtract") => returns 3
ArithmeticFunction.arithmetic(5, 2, "multiply") => returns 10
ArithmeticFunction.arithmetic(5, 2, "divide")   => returns 2
```

Try to do it without using if statements!
def arithmetic(a, b, operator):
    opd = {'add': a+b,'subtract': a-b,'multiply': a*b,'divide': a/b}
    return opd[operator]