inconsistency with += between different types ?

[Donn Cave]

Quoth Andreas.Leitgeb at siemens.at (Andreas Leitgeb):
...
| Because += already has this fallback to __add__ builtin, __iadd__ 
|   shouldn't care about the immutable case. It need not even exist for 
|   that case.   Now for the mutable case, it should be __iadd__'s only
|   job to get the mutation done on the object.

This would force the programmer to rely on the absence of __iadd__
to implicitly get the desired behavior.  It's clearer (and faster,
cf. Timothy Delaney's followup) to make it explicit.

	Donn Cave, donn at u.washington.edu