gh-135307: Fix email error when policy max_line_length is set to 0 or None by zangjiucheng · Pull Request #135367 · python/cpython

zangjiucheng · 2025-06-10T22:15:21Z

Issue: Unexpected exceptions when email.policy.Policy.max_line_length is falsey #135307

[pull] main from python:main

ZeroIntensity

Triage silliness

Lib/test/test_email/test_message.py

ZeroIntensity · 2025-06-10T23:26:24Z

Misc/NEWS.d/next/Library/2025-06-10-18-02-29.gh-issue-135307.fXGrcK.rst

+:mod:`email`: Ensure policy accepts unlimited line lengths by
+treating 0 or :const:`None` as :data:`sys.maxsize`


Suggested change

:mod:`email`: Ensure policy accepts unlimited line lengths by

treating 0 or :const:`None` as :data:`sys.maxsize`

:mod:`email`: Ensure policy accepts unlimited line lengths by

treating 0 or :const:`None` as :data:`sys.maxsize`.

I would phrase this as follows: "Fix exception in set_content when encoding text and max_line_length is set to 0 or None (unlimited)." maxsize is an implementation detail and not appropriate for a news item. And it's not the policy that isn't accepting the unlimited line lengths, it's set_content ;)

Makes sense to me, we can keep implementation detail behind :)

zangjiucheng · 2025-06-10T23:53:12Z

Haha, nice catch lol

Lib/test/test_email/test_message.py

picnixz

Some comments. I'll review more on my laptop.

Lib/email/contentmanager.py

Lib/test/test_email/test_message.py

Misc/NEWS.d/next/Library/2025-06-10-18-02-29.gh-issue-135307.fXGrcK.rst

zangjiucheng · 2025-06-19T14:49:06Z

@picnixz Thanks for your detailed review. I addressed all the issues you mentioned in the new commit.

Lib/test/test_email/test_message.py

Lib/email/contentmanager.py

picnixz · 2025-06-19T15:08:00Z

Lib/email/contentmanager.py

    if cte is None:
        # Use heuristics to decide on the "best" encoding.
-        if max((len(x) for x in lines), default=0) <= policy.max_line_length:
+        if max((len(x) for x in lines), default=0) <= maxlen:


We can use: max(map(len, lines), default=0), though I'm not sure which is the fastest and which is the most "readable".

@bitdancer What is the style you'd recommend in general in the email package? would you rather for readability, succintness, or performance?

Just my comment: we're not required to take the fastest route here, since we may not have a heavy load on the email module. Still wish to hear more comments before we resolve this :)

Well, mailman can put a pretty heavy load on the email package, and it is one of the biggest consumers of the package. While I know there are opportunities for performance improvements in the new email code that I haven't gotten around to investigating, I personally tend to do what others call micro-optimizations when I notice them[*], unless they make the code really hard to understand. Not that I know which is faster, here.

[*] I read an article once where Knuth felt his comment had been misinterpreted, and pointed out that if you routinely ignore optimization opportunities you pretty quickly end up with a really slow program.

[*] I read an article once where Knuth felt his comment had been misinterpreted, and pointed out that if you routinely ignore optimization opportunities, you pretty quickly end up with a really slow program.

@bitdancer Thanks for sharing the additional context — it’s really helpful to know there’s a concrete performance impact for real users like Mailman.

I agree that starting with small, focused micro-optimizations makes sense, especially since we’re planning a broader optimization pass for the email module.

I’ve incorporated your suggestion and updated the comment in the code accordingly.
Please also let me know if you have any specific areas you think would benefit most from further optimization work. Hope to collaborate on more work with you!

FTR, I don't think this will change much because we've seen times when code is slower with an map() and sometimes slower with a comprehension. If we want to make the code faster, we should run better benchmarks.

Lib/test/test_email/test_message.py

zangjiucheng · 2025-07-10T00:38:08Z

Hi everyone, sorry to bother you. Is there any update on this PR?

Lib/email/contentmanager.py

Lib/test/test_email/test_message.py

bitdancer · 2025-11-01T20:11:19Z

I couldn't figure out how to get review mode to show me all the conversations, so I made individual comments in conversation mode. Sorry if that makes more work for others, or if I ended up with misplaced comments.

zangjiucheng · 2025-11-01T20:35:46Z

@bitdancer No worries, I saw all your comments and I will address them one by one later today.

bitdancer

LGTM, thanks.

miss-islington-app · 2025-11-02T14:32:18Z

Thanks @zangjiucheng for the PR, and @bitdancer for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

…o 0 or None (pythonGH-135367) (cherry picked from commit 6d45cd8) Co-authored-by: Jiucheng(Oliver) <git.jiucheng@gmail.com> RDM: Like the change made in a earlier PR to the folder, we can/must use 'maxlen' as a stand in for 'unlimited' when computing line lengths when max_line_length is 0 or None; otherwise the computation results in a traceback.

miss-islington-app · 2025-11-02T14:32:25Z

Sorry, @zangjiucheng and @bitdancer, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 6d45cd8dbb07ae020ec07f2c3375dd06e52377f6 3.13

bedevere-app · 2025-11-02T14:32:26Z

GH-140915 is a backport of this pull request to the 3.14 branch.

…s set to 0 or None (pythonGH-135367) (cherry picked from commit 6d45cd8) Co-authored-by: Jiucheng(Oliver) <git.jiucheng@gmail.com> RDM: Like the change made in a earlier PR to the folder, we can/must use 'maxlen' as a stand in for 'unlimited' when computing line lengths when max_line_length is 0 or None; otherwise the computation results in a traceback.

bedevere-app · 2025-11-02T14:48:20Z

GH-140917 is a backport of this pull request to the 3.13 branch.

…to 0 or None (GH-135367) (#140915) gh-135307: Fix email error when policy max_line_length is set to 0 or None (GH-135367) (cherry picked from commit 6d45cd8) RDM: Like the change made in a earlier PR to the folder, we can/must use 'maxlen' as a stand in for 'unlimited' when computing line lengths when max_line_length is 0 or None; otherwise the computation results in a traceback. Co-authored-by: Jiucheng(Oliver) <git.jiucheng@gmail.com>

…to 0 or None (GH-135367) (#140917) [3.13] gh-135307: Fix email error when policy max_line_length is set to 0 or None (GH-135367) (cherry picked from commit 6d45cd8) Co-authored-by: Jiucheng(Oliver) <git.jiucheng@gmail.com> RDM: Like the change made in a earlier PR to the folder, we can/must use 'maxlen' as a stand in for 'unlimited' when computing line lengths when max_line_length is 0 or None; otherwise the computation results in a traceback.

…o 0 or None (python#135367) RDM: Like the change made in a earlier PR to the folder, we can/must use 'maxlen' as a stand in for 'unlimited' when computing line lengths when max_line_length is 0 or None; otherwise the computation results in a traceback.

zangjiucheng added 2 commits June 8, 2025 10:58

Merge pull request #169 from python/main

a210d49

[pull] main from python:main

enhance email content handling: allow infinite line length in encoding

e9de710

zangjiucheng requested a review from a team as a code owner June 10, 2025 22:15

bedevere-app bot added the awaiting review label Jun 10, 2025

bedevere-app bot mentioned this pull request Jun 10, 2025

Unexpected exceptions when email.policy.Policy.max_line_length is falsey #135307

Closed

Fix lint

0a5f379

zangjiucheng changed the title ~~gh-135307: Support email unlimited line lengths when policy max_line_length is 0 or None~~ gh-135307: Fix email error when policy max_line_length is set to 0 or None Jun 10, 2025

ZeroIntensity added topic-email needs backport to 3.13 bugs and security fixes needs backport to 3.14 bugs and security fixes labels Jun 10, 2025

ZeroIntensity reviewed Jun 10, 2025

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fix: correct formatting in email test cases and NEWS entry

d0dc3c0

efimov-mikhail reviewed Jun 11, 2025

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Lib/test/test_email/test_message.py Outdated Show resolved Hide resolved

picnixz reviewed Jun 19, 2025

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Update NEWS entry, test case enhance, lint code

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zangjiucheng requested a review from picnixz June 19, 2025 14:50

efimov-mikhail reviewed Jun 19, 2025

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picnixz reviewed Jun 19, 2025

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resort import; restructure testcase

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picnixz reviewed Jun 19, 2025

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picnixz reviewed Jun 19, 2025

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zangjiucheng added 2 commits June 19, 2025 13:29

tiny enhance varaible

603ff74

Tiny update for test case for better readability

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efimov-mikhail reviewed Jul 12, 2025

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test: update test assertion for line wrapping in email messages

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bitdancer mentioned this pull request Nov 1, 2025

bpo-34800: Fix email.contentmanager raise error when policy.max_line_length is 0 or None #9578

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zangjiucheng added 2 commits November 1, 2025 20:52

perf(email): optimize max line length calculation

c24ec76

docs: improve formatting in email module NEWS entry

befa25d

bitdancer approved these changes Nov 2, 2025

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bedevere-app bot added awaiting merge and removed awaiting review labels Nov 2, 2025

bitdancer merged commit 6d45cd8 into python:main Nov 2, 2025
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bedevere-app bot removed the awaiting merge label Nov 2, 2025

miss-islington-app bot assigned bitdancer Nov 2, 2025

bedevere-app bot removed the needs backport to 3.14 bugs and security fixes label Nov 2, 2025

bedevere-app bot removed the needs backport to 3.13 bugs and security fixes label Nov 2, 2025

		:mod:`email`: Ensure policy accepts unlimited line lengths by
		treating 0 or :const:`None` as :data:`sys.maxsize`

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zangjiucheng commented Jun 10, 2025 •

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