It would be nice to have an additional argument for str.join() so this

", ".join(["a", "b", "c"], ", and ")

would output

"a, b, and, c"

This seems like a very specific use case. Too specific IMO for a method on all string objects for anyone using Python anywhere in the world. Why not just write a function like this?

    def my_join(strings, sep=", ", last_sep=", and "):
        strings = list(strings)
        return sep.join(strings[:-1]) + last_sep + strings[-1]

    >>> my_join(["one", "two", "three"])
    'one, two, and three'

Python 3.9 is in feature freeze, this couldn't be added before 3.10 now.

You have:

    ", ".join(["a", "b", "c"], ", and ")

outputing this:

"a, b, and, c"

So what are the semantics of this additional argument? To insert it before the last item?

Looking more closely, I think that the semantics are to concatenate the extra argument to the second-last item:

    ", ".join(["a", "b", "c"])
    # -> "a, b, c"

    ", ".join(["a", "b", "c"], ", and")
    # -> "a, b, and, c"

which would be the same as:

    ", ".join(["a", "b, and", "c"])
    # -> "a, b, and, c"


I'm not sure how this is useful. In English, there should never be a comma after the "and", and there possibly shouldn't be a comma after the "b" either, depending on context.

    # Should be: "a, b and c" or "a, b, and c"

See the Oxford or serial comma:

https://thegrammargirls.wordpress.com/tag/oxford-comma/


I'm going to close this feature request. It's too specific and the semantics don't seem to be very useful. But if you would still like to propose this, or a similar change, please discuss it first either on the Python-Ideas mailing list:

    https://mail.python.org/archives/list/python-ideas@python.org/


or at the Ideas topic on

    https://discuss.python.org


so that we can determine the required semantics and get a sense for how useful it would be in general.