[New-bugs-announce] [issue32010] Multiple get "itemgetter"

[Mario Corchero]

New submission from Mario Corchero <mariocj89 at gmail.com>:

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)
<Mock name='mock.child1.child2' id='4317895480'>

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

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components: Library (Lib)
messages: 306114
nosy: mariocj89
priority: normal
severity: normal
status: open
title: Multiple get "itemgetter"
type: enhancement
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32010>
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