On 22Apr2019 2119, Glenn Linderman wrote:
While Inada's suggested DictBuilder interface was immediately obvious, I don't get how either copy or update would achieve the goal. Perhaps you could explain? Particularly, what would be the trigger that would make dict() choose to create a shared key dictionary from the start? Unless it is known that there will be lots of (mostly static) dictionaries with the same set of keys at the time of creation of the first one, creating a shared key dictionary in every case would cause later inefficiencies in converting them, when additional items are added? (I'm assuming without knowledge that a single shared key dictionary is less efficient than a single regular dictionary.)
Passing a dictionary to the dict() constructor creates a copy of that dictionary (as does copy.copy()). What other trigger do you need to decide "it contains the same keys"? It's a copy of the original dict, so by definition at that point it may as well share its entire contents with the original.
Basically this is just a partial copy-on-write, where we copy values eagerly - since they're almost certainly going to change - and keys lazily - since there are known scenarios where they are not going to be changed, but we'll pay the cost later if it turns out they are.
Cheers, Steve _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
