[Python-Dev] Proposal: dict.with_values(iterable) (original) (raw)

Victor Stinner vstinner at redhat.com
Fri Apr 12 10:31:47 EDT 2019

Nice optimization! I have questions on the proposed API.

withvalues(self, iterable, /) Create a new dictionary with keys from this dict and values from iterable.

When length of iterable is different from len(self), ValueError is raised. This method does not support dict subclass.

In short, mydict.with_values(values) behaves as dict(zip(mydict.keys(), values)), but is more efficient?

The method rely on the fact that dict is preserving key insertion order, right?

Le ven. 12 avr. 2019 à 15:47, Inada Naoki <songofacandy at gmail.com> a écrit :

This might be usable for:

* csv.DictReader * namedtuple.asdict() * DB-API 2.0 implementations: (e.g. DictCursor of mysqlclient-python)

I guess that a new dict constructor taken keys and values like dict.from_keys_and_values(keys, values) would work, but would not benefit from the dict key-sharing optimization?

Would it be possible to implement the key-sharing optimization using a dict.from_keys_and_values(mydict.keys(), values) method: detect that keys are owned by a dict, and so create a new dict linked to the keys dict? A dict view contains a reference to the iterated dict (dictiterobject.di_dict).

I'm fine with dict.with_values() API, but I'm asking if it could be written differently.

Victor

Night gathers, and now my watch begins. It shall not end until my death.

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