On 2/20/06, Dan Gass <[EMAIL PROTECTED]> wrote: > Why not have the factory function take the key being looked up as an > argument?
This was considered and rejected already. You can already customize based on the key by overriding on_missing() [*]. If the factory were to take a key argument, we couldn't use list or int as the factory function; we'd have to write lambda key: list(). There aren't that many use cases for having the factory function depend on the key anyway; it's mostly on_missing() that needs the key so it can insert the new value into the dict. [*] Earlier in this thread I wrote that on_missing() could be inlined. I take that back; I think it's better to have it be available explicitly so you can override it without having to override __getitem__(). This is faster, assuming most __getitem__() calls find the key already inserted, and reduces the amount of code you have to write to customize the behavior; it also reduces worries about how to call the superclass __getitem__ method (catching KeyError *might* catch an unrelated KeyError caused by a bug in the key's __hash__ or __eq__ method). -- --Guido van Rossum (home page: http://www.python.org/~guido/) _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
