I have the following function. Ideally, I want to have either a single string or a list of strings passed as an input. In either case, I need to use .upper on it. But, when only a single string is passed, the iterator iterates through each character. How can I have an if statement that tests whether a list of strings or a single string? (I can't seem to avoid the iterable nature of strings)

```
def runthis(stringinput):

    for t in stringinput:
        t = t.upper()

```