Join split words and punctuation with punctuation in the right place

So I tried using join() after splitting a string into words and punctuation but it joins the string with a space in between the word and punctuation.

b = ['Hello', ',', 'who', 'are', 'you', '?']
c = " ".join(b)

But that returns:
c = 'Hello , who are you ?'

and I want:
c = 'Hello, who are you?'

You could join on the punctuation first:

def join_punctuation(seq, characters='.,;?!'):
    characters = set(characters)
    seq = iter(seq)
    current = next(seq)

    for nxt in seq:
        if nxt in characters:
            current += nxt
        else:
            yield current
            current = nxt

    yield current

c = ' '.join(join_punctuation(b))

The join_punctuation generator yields strings with any following punctuation already joined on:

>>> b = ['Hello', ',', 'who', 'are', 'you', '?']
>>> list(join_punctuation(b))
['Hello,', 'who', 'are', 'you?']
>>> ' '.join(join_punctuation(b))
'Hello, who are you?'