I want to prohibit certain operators being used in a function, for example, say I want to make sure the `**` power operator is not being used in the following function: 

```
def pow(x, y):
    return x ** y

```

I have used `inspect.getsource` to get the source and checked if `"**"` is in the source but that will wrongly cause an assert error if there happens to be `"**"` in the source elsewhere so how to actually check the code for the existence of a particular operator?