Description

sayandipdutta

opened on Oct 24, 2024

Issue body actions

Feature or enhancement

Proposal:

functools.reduce takes function (generally a callable) and iterable, with an optional initial parameter:

https://docs.python.org/3/library/functools.html#functools.reduce

However, initial cannot be passed as a keyword argument, which reduces ;) readability,

from functools import reduce
from operator import sub
>>> reduce(sub, [1, 1, 2, 3, 5, 8], 21)
1
>>> reduce(sub, [1, 1, 2, 3, 5, 8], initial=21)
TypeError: reduce() takes no keyword arguments

Allowing initial as keyword argument will be more clear, and initial could also be passed as a keyword argument while making partial functions out of reduce.

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/remove-positional-only-restriction-on-initial-parameter-of-reduce/68897

Linked PRs

• gh-125916: Allow functools.reduce 'initial' to be a keyword argument #125917
• gh-125916: Adapt functools.reduce() to Argument Clinic #125999

Activity

1. sayandipdutta

   added

   type-featureA feature request or enhancementA feature request or enhancement

   on Oct 24, 2024
2. skirpichev commented on Oct 24, 2024

   

   skirpichev

   on Oct 24, 2024

   Member

   More actions

   See also #121677
3. skirpichev commented on Oct 24, 2024

   

   skirpichev

   on Oct 24, 2024

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   More actions

   Also see #96640.

   @sobolevn, did you actually try to do conversion and benchmark it?
4. skirpichev

   added a commit that references this issue on Oct 26, 2024

   pythongh-125916: convert reduce() to Argument Clinic

   b5ac476
5. erlend-aasland

   added a commit that references this issue on Nov 1, 2024

   gh-125916: Adapt functools.reduce() to Argument Clinic (#125999)

   51ef54a
6. erlend-aasland

   added

   extension-modulesC modules in the Modules dirC modules in the Modules dir

   on Nov 1, 2024
7. erlend-aasland

   linked a pull request that will close this issuegh-125916: Allow functools.reduce 'initial' to be a keyword argument #125917on Nov 12, 2024
8. erlend-aasland

   added a commit that references this issue on Nov 12, 2024

   gh-125916: Allow functools.reduce() 'initial' to be a keyword argument (

   abb90ba
9. erlend-aasland

   closed this as completedin #125917on Nov 12, 2024
10. picnixz

    added 2 commits that reference this issue on Dec 8, 2024

    pythongh-125916: Adapt functools.reduce() to Argument Clinic (python#…

    a156925

    pythongh-125916: Allow functools.reduce() 'initial' to be a keyword a…

    86ef3e4
11. ebonnal

    added 2 commits that reference this issue on Jan 12, 2025

    pythongh-125916: Adapt functools.reduce() to Argument Clinic (python#…

    14e5e9f

    pythongh-125916: Allow functools.reduce() 'initial' to be a keyword a…

    17efa6e
12. skirpichev

    marked functools.reduce does not accept keyword arguments for its parameters #139114 as a duplicate of this issue on Sep 18, 2025

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