Issue 32010: Multiple get "itemgetter" (original) (raw)

Issue32010

Created on 2017-11-12 14:49 by mariocj89, last changed 2022-04-11 14:58 by admin. This issue is now closed.

Messages (3)
msg306114 - (view)	Author: Mario Corchero (mariocj89) *	Date: 2017-11-12 14:49
At the moment we can get an operator that performs multiple "gets" in object attributes. Example: >>> getter = operator.attrgetter("child1.child2") >>> o = mock.Mock() >>> getter(o) On the other hand, itemgetter -which can be used for mappings- can only access single level. a = itemgetter("a")(d) The proposal is to add a way to perform multiple fetches the say way attrgetter is doing it. The main worry here for me would be that it might break some existing callers if someone had "a.b" as a key in a dict and were using itemgetter. An option might be a new argument separator to split those so it'd look like: d = dict(a=dict(b=1), b=dict(c=2)) ab = itemgetter("a.b", separator=".")(d) This is effectively sugar for: itemgetter("b")(itemgetter("a")(d)) This should be available in the *args version as well so the following is valid: d = dict(a=dict(b=1), b=dict(c=2)) ab, ac = itemgetter("a.b", "b.c", separator=".")(d) This is coming from python-dev mailing list thread: "[Python-Dev] Analog of PEP 448 for dicts (unpacking in assignment with dict rhs)" I have a sample implementation on the py side. If this is interesting I can send a PR with the full impl (I havent started yet with the C one) If anyone is interested in the ongoing implementation: https://github.com/mariocj89/cpython/tree/multiple_itemgetter
msg306115 - (view)	Author: Serhiy Storchaka (serhiy.storchaka) *	Date: 2017-11-12 15:32
As you have said, this will break existing code. And this is not applicable to non-string indices. I think that it would be easier to use a lambda or local function for this: `lambda x: x['a']['b']`. It is shorter and cleaner. I don't see how this is related to the Python-Dev thread.
msg306140 - (view)	Author: Raymond Hettinger (rhettinger) *	Date: 2017-11-13 05:42
I also don't think this should be done to itemgetter() which should remain focused on its core task. Thank you for the suggestion, but am marking this as closed. Perhaps consider posting a recipe to the ASPN cookbook (I've posted a lot of ideas there) or publish something on PyPI to see if there is any uptake.