More comments about dict-like objects in Python:
- do not use .keys() whenever you don't need a list copy of keys
- do not implement a has_key method that would only be an alias of __contains__ (btw, there's still a lot of uses on dict.has_key in ERP5 and they should be replaced by in)
- do not implement a get method that calls __getitem__ unless it is used often; if performance is important, you may consider to duplicate the code of __getitem__
- similarly, we could remove the keymethod: the caller could still cast to list

/suggested by @jm