Description

inventshah

opened on Mar 29, 2026

Issue body actions

Bug report

Bug description:

In the 3.15 alphas, the + operator does not dispatch to obj.__radd__ when the left hand object inherits from a sequence like class (list, tuple, ...), but does if it is a base instance.

class A:
    def __radd__(self, other): ...

class B(tuple): ...

() + A()  # No error
B() + A() # TypeError: can only concatenate tuple (not "A") to tuple

I originally ran into the issue with a NamedTuple, but looks like subclasses of array.array, bytearray, bytes, collections.deque, list, str, and tuple all raise the error.

Works in 3.14.3. git bisect'd to e6e376a, so something in the resolution between nb_add and sq_concat may have changed while optimizing (* has a similar problem with __rmul__ mapping to nb_multiply and sq_repeat).

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-146587: fix type slot assignment incase of multiple slots for same name #146593

Reacted by Clément Robert

Activity

1. inventshah

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Mar 29, 2026
2. inventshah commented on Mar 29, 2026

   

   inventshah

   on Mar 29, 2026

   ContributorAuthor

   More actions

   cc @sergey-miryanov as the bisect'd PR author
3. picnixz

   added

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   3.15bugs and security fixesbugs and security fixes

   release-blocker

   on Mar 29, 2026
4. github-project-automation

   added this to Release and Deferred blockers 🚫on Mar 29, 2026
5. github-project-automation

   moved this to Todo in Release and Deferred blockers 🚫on Mar 29, 2026
6. sergey-miryanov commented on Mar 29, 2026

   

   sergey-miryanov

   on Mar 29, 2026

   Contributor

   More actions

   Will take a look soon
7. serhiy-storchaka commented on Mar 29, 2026

   

   serhiy-storchaka

   on Mar 29, 2026

   Member

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   cc @JelleZijlstra, @vstinner
8. serhiy-storchaka

   added

   3.14bugs and security fixesbugs and security fixes

   and removed

   3.14bugs and security fixesbugs and security fixes

   on Mar 29, 2026
9. neutrinoceros

   marked right operand's __radd__ method is ignored when the left operand is a NamedTuple (3.15.0a7) #146592 as a duplicate of this issue on Mar 29, 2026
10. kumaraditya303 commented on Mar 29, 2026

    

    kumaraditya303

    on Mar 29, 2026

    Contributor

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    I'm working on a fix.

    Reacted by Clément Robert
11. kumaraditya303 commented on Mar 29, 2026

    

    kumaraditya303

    on Mar 29, 2026

    Contributor

    More actions

    PR #146593 fixes this.
12. kumaraditya303

    added a commit that references this issue on Mar 29, 2026

    Merge branch 'fix-pythongh-146587' of https://github.com/kumaraditya3…

    8be175f
13. kumaraditya303

    moved this from Todo to In Progress in Release and Deferred blockers 🚫on Mar 29, 2026
14. kumaraditya303

    added a commit that references this issue on Mar 30, 2026

    gh-146587: fix type slot assignment incase of multiple slots for same…

    8e10bd7
15. kumaraditya303

    closed this as completedon Mar 30, 2026
16. github-project-automation

    moved this from In Progress to Done in Release and Deferred blockers 🚫on Mar 30, 2026
17. maurycy

    added a commit that references this issue on Mar 30, 2026

    Merge remote-tracking branch 'upstream/main' into tachyon-ndjson-kole…

    6a0ea81
18. clin1234

    added a commit that references this issue on Apr 16, 2026

    pythongh-146587: fix type slot assignment incase of multiple slots fo…

    b3eeeb8
19. ljfp

    added a commit that references this issue on Apr 25, 2026

    pythongh-146587: fix type slot assignment incase of multiple slots fo…

    b369302

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