[Python-ideas] Allow using ** twice

[Stephen J. Turnbull]

Andrew Barnert writes:
 > On Jun 6, 2013, at 8:43, Haoyi Li <haoyi.sg at gmail.com> wrote:

 > There should be one way to do it...I'd agree except, well, there
 > are two different things that people want to do here!

 > Actually, there's three:

Four: associate a multivalue containing all of the individual values
to the key (sort of a set-valued Counter).  (This comes up in practice
in applications that assume UUIDs on the Internet, especially in mail.
For example, when I receive a post via both a mailing list and a
personal copy, eventually I want to save the mailing list's version in
preference to the personal copy.  But I only want to display one
version in the MUA.  In archiving, you run into the occasional author
who provides their own non-unique message ID conflicting with a
*different* message.  Etc.)

And somebody was just asking for Counter addition.  Counter is a dict
subclass, so "dict(...) + dict(...) = updated_dict" would imply really
perverse semantics for "Counter(...) + Counter(...)".

How about extending .update to take multiple positional arguments?
Then TOOWTDI idiom would be

    {}.update(d1, d2, ...)

The "first found wins" interpretation could use a different method:

    {}.extend(d1, d2, ...)