magical expanding hash

[braver]

Thanks, James!  This is really helpful.

: It would take a lot of coding to make that << work right. Better is
the pythonic
:
: m[key] = [value]
:
: Its really only one more keystroke than
:
: m[key] << value

But it's only for the first element, right?  I'd have to say
meh[key1]...[keyN].append(elem2) after that, while I want an operator
to look the same.

Also, what's the shortest python idiom for get_or_set in expression?
E.g., when creating a numeric leaf, I'd say

if meh.has_key('a'): meh['a'] += 7
else: meh['a'] = 7

-- but I'd have to do it everywhere!  That's why I'd like to override
+= to do the check/init for me.