What's the best way to return multiple values from a function?

def f(in_str):
    out_str = in_str.upper()
    return True, out_str # Creates tuple automatically

succeeded, b = f("a") # Automatic tuple unpacking

Why not throw an exception if the operation wasn't successful? Personally, I tend to be of the opinion that if you need to return more than one value from a function, you should reconsider if you're doing things the right way or use an object.

But more directly to the point, if you throw an exception, you're forcing them to deal with the problem. If you try to return a value that indicates failure, it's very well possible somebody could not check the value and end up with some potentially hard to debug errors.

Return a tuple.

def f(x):
    # do stuff
    return (True, modified_string)

success, modified_string = f(something)

Returning a tuple is the usual way to do this in Python.