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PEP 795: Deep Immutability in Python #4468

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@TobiasWrigstad TobiasWrigstad commented Jun 19, 2025 •
edited by hugovk
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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
  • 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
    • Rationale
    • Specification
    • Backwards Compatibility
    • Security Implications
    • How to Teach This
    • Reference Implementation
    • Rejected Ideas
    • Open Issues
  • Python-Version set to valid (pre-beta) future Python version, if relevant
  • Any project stated in the PEP as supporting/endorsing/benefiting from the PEP formally confirmed such
  • Right before or after initial merging, PEP discussion thread created and linked to in Discussions-To and Post-History

📚 Documentation preview 📚: https://pep-previews--4468.org.readthedocs.build/pep-0795/

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@TobiasWrigstad TobiasWrigstad requested a review from a team as a code owner June 19, 2025 06:16
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python-cla-bot bot commented Jun 19, 2025 •
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All commit authors signed the Contributor License Agreement.

CLA signed

@AA-Turner AA-Turner changed the title (削除) PEP 795: Add deep immutability to Python (削除ここまで) (追記) PEP 795: Deep Immutability in Python (追記ここまで) Jun 19, 2025
@AA-Turner AA-Turner added the new-pep A new draft PEP submitted for initial review label Jun 19, 2025
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Is there a programmatic/text source that this file was created from? If so, it would be useful to include that, and also consider using an SVG file rather than a PNG.

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@TobiasWrigstad TobiasWrigstad Jun 19, 2025

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Hmm. We followed PEP12 which says:

peps/peps/pep-0012.rst

Lines 604 to 605 in b5ae2b1

Currently, SVG must be avoided due to compatibility issues with the
PEP build system.

Maybe this is outdated instructions?

Currently the file was extracted from Keynote which is macOS-only. We could redraw this in a more accessible format perhaps.

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Yes, we can now support & prefer SVG files. If Keynote will export an SVG, that should be fine? I had wondered if you'd used e.g. TikZ or graphviz to make the image.

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Please avoid force pushing, we squash-merge all PRs.
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hugovk commented Jun 19, 2025 •
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For the next PEP, please wait until the initial PR is merged before opening the PEP discussion, because we want to share the official peps.python.org URL and not the PR preview that will be deleted at some point. (Pre-PEP discussions can be opened at any time.)

And especially please wait until the sponsor had confirmed sponsorship, as we the PEP number only gets officially assigned then and it can cause confusion to re-assign numbers later.

Please see PEP 1 for more details.

https://peps.python.org/pep-0001/#submitting-a-pep

Thank you!
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Co-authored-by: Michael Droettboom <mdboom@gmail.com>

3. The type ``NotFreezable`` which is an empty type which cannot be made immutable and can be used as a super class to classes whose instances should not be possible to freeze

4. The type ``NotFreezableError`` which is raised on an attempt to mutate an immutable object
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Isn't this for an attempt to freeze and unfreezable object? Below, it says it raises a TypeError when trying to mutate an immutable object.

mjp41 and others added 5 commits December 19, 2025 12:05 
See "Changes from the previous draft" for details.
--
Co-authored-by: Tobias Wrigstad <tobias.wrigstad@it.uu.se>
Co-authored-by: Fridtjof Stoldt <xFrednet@gmail.com>
Co-authored-by: Matthew Johnson <matajoh@users.noreply.github.com>

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TobiasWrigstad and others added 7 commits December 19, 2025 17:21 
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Thanks to Cornelius Krupp for pointing these out.
As pointed out by Cornelius Krupp, types created
by the namedtuple constructor are mutable.
* Added subclass info; clarified explicit objects
* Bug fixes in the RST
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