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PEP 837: Extensible JSON serialization#5031

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serhiy-storchaka:pep-837-extensible-json
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PEP 837: Extensible JSON serialization#5031
serhiy-storchaka wants to merge 10 commits into
python:mainfrom
serhiy-storchaka:pep-837-extensible-json

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@serhiy-storchaka

@serhiy-storchaka serhiy-storchaka commented Jul 12, 2026 •
edited by jeremyhylton
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New PEP proposing an extension mechanism for the json encoder at
three levels: the __json__()/__raw_json__() protocol (library
level), a copyreg.json() registry following the copyreg.pickle()
precedent (application level), and a per-encoder dispatch_table
attribute mirroring pickle.Pickler (call level).

Reference implementation: python/cpython branch json-customize4
(link: https://github.com/serhiy-storchaka/cpython/tree/json-customize4).

The idea has been discussed repeatedly since 2010; see the PEP's
Motivation for the tracker issues and the python-ideas /
discuss.python.org threads:
2010,
2019,
2020,
2022 (registry),
2022–2024 (__json__).

Basic requirements (all PEP Types)

  • Read and followed PEP 1 & PEP 12
  • File created from the latest PEP template
  • PEP has next available number, & set in filename (pep-NNNN.rst), PR title (PEP 123: <Title of PEP>) and PEP header
  • Title clearly, accurately and concisely describes the content in 79 characters or less
  • Core dev/PEP editor listed as Author or Sponsor, and formally confirmed their approval
  • Author, Status (Draft), Type and Created headers filled out correctly
  • PEP-Delegate, Topic, Requires and Replaces headers completed if appropriate (none applicable)
  • Required sections included
    • Abstract (first section)
    • Copyright (last section; exact wording from template required)
  • Code is well-formatted (PEP 7/PEP 8) and is in code blocks, with the right lexer names if non-Python
  • PEP builds with no warnings, pre-commit checks pass and content displays as intended in the rendered HTML
  • Authors/sponsor added to .github/CODEOWNERS for the PEP

Standards Track requirements

  • PEP topic discussed in a suitable venue with general agreement that a PEP is appropriate
  • Suggested sections included (unless not applicable)
    • Motivation
    • Specification
    • Rationale
    • Backwards Compatibility
    • Security Implications
    • How to Teach This
    • Reference Implementation
    • Rejected Ideas
    • Open Issues

🤖 Generated with Claude Code

@serhiy-storchaka @claude
PEP 837: Extensible JSON serialization
6f50b34 
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
@serhiy-storchaka serhiy-storchaka requested a review from a team as a code owner July 12, 2026 05:49
@serhiy-storchaka serhiy-storchaka mentioned this pull request Jul 12, 2026
Draft
@serhiy-storchaka @claude
PEP 837: Link the reference implementation PR
3725ee1 
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
@read-the-docs-community

read-the-docs-community Bot commented Jul 12, 2026 •
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Documentation build overview

📚 pep-previews | 🛠️ Build #33624417 | 📁 Comparing 00de144 against latest (339af2b)

  🔍 Preview build  

11 files changed · + 3 added · ± 8 modified

+ Added

± Modified

@serhiy-storchaka @claude
PEP 837: Add Discussions-To and Post-History
4256286 
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
@serhiy-storchaka

serhiy-storchaka commented Jul 12, 2026

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Discussion thread: https://discuss.python.org/t/pep-837-extensible-json-serialization/108124 (Discussions-To and Post-History headers added).

hugovk
hugovk reviewed Jul 12, 2026
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I probably won't have time for a full review due to EuroPython, here's a couple of suggestions.

Comment thread peps/pep-0837.rst
Discussions-To: https://discuss.python.org/t/pep-837-extensible-json-serialization/108124
Status: Draft
Type: Standards Track
Created: 11-Jul-2026

@hugovk hugovk Jul 12, 2026

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Suggested change
Created: 11-Jul-2026
Created: 12-Jul-2026

@serhiy-storchaka serhiy-storchaka Jul 12, 2026

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I wrote it 11-Jul-2026, but submitted next morning 12-Jul-2026. What counts?

@hugovk hugovk Jul 16, 2026

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It's the day the PEP number is assigned.

Sometimes PEPs are written months ago and iterated upon before a PR is opened and a number assigned.

Comment thread peps/pep-0837.rst Outdated
Comment thread peps/pep-0837.rst Outdated
Comment thread peps/pep-0837.rst Outdated
serhiy-storchaka and others added 2 commits July 12, 2026 12:47
@serhiy-storchaka @claude
PEP 837: Cite simplejson issue 52 for the for_json naming rationale
c3f19bd 
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
@serhiy-storchaka @claude
PEP 837: Use the cpython-issue role for issue references
d745835 
Also fix the markup of the '__raw_json__ as a pure marker' bullet
(inline markup cannot be nested) and escape numpy.bool_ in the
appendix.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
@serhiy-storchaka

serhiy-storchaka commented Jul 12, 2026

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Thank you. Fixed rendering and modernized cpython-issue references.

@serhiy-storchaka serhiy-storchaka mentioned this pull request Jul 12, 2026
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@konsti-openai konsti-openai mentioned this pull request Jul 15, 2026
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serhiy-storchaka and others added 2 commits July 16, 2026 22:10
@serhiy-storchaka @claude
PEP 837: Renumber to 841
8292cf4 
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
@serhiy-storchaka
Merge remote-tracking branch 'origin/main' into pep-837-extensible-json
8b87d4f 
# Conflicts:
#	.github/CODEOWNERS
@serhiy-storchaka serhiy-storchaka changed the title PEP 837: Extensible JSON serialization PEP 841: Extensible JSON serialization Jul 16, 2026
@serhiy-storchaka @claude
PEP 841: Renumber back to 837
900771e 
PEP 837 was freed for this PEP's earlier claim when the conflicting
PEP was renumbered to 840 in python#5043.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
@serhiy-storchaka serhiy-storchaka changed the title PEP 841: Extensible JSON serialization PEP 837: Extensible JSON serialization Jul 16, 2026
serhiy-storchaka and others added 2 commits July 16, 2026 22:28
hugovk
hugovk approved these changes Jul 16, 2026
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Approved with date change, thanks! :)

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