[patch] Add convenience methods to SortedDict

[Paul Collier <paul@…>]

When generating dynamic fields for a newforms form it is convenient to have a few more SortedDict methods (particularly insert(), which is not entirely trivial) for DRY.

[Chris Beaven]

Seems useful, what does core think?

[Malcolm Tredinnick]

Seems reasonable. We should check this really does implement all the useful dictionary methods and get it right -- rather than just implementing the ones Paul needs right now.

I don't think the insert() method is needed, though. SortedDict is sorted by insert order, not by anything else, so inserting out of order seems to go against the grain.

[Paul Collier <paul@…>]

Hmm, okay... I was using that to dynamically insert a field at the top of a Form I was using. If it violates what's expected, don't worry about it; either I'll come up with something else or just continue to patch it solely on my installation :)

[Fredrik Lundh <fredrik@…>]

I think "insert" makes sense (there's already a "value_for_index" method, which breaks the "dictness" of this class). Maybe it could be called "insert_at_index"?

[Malcolm Tredinnick]

(In [6350]) Fixed #3993 -- Added some useful dictionary methods to SortedDict, plus an insert() method. Patch from Paul Collier.