bpo-28598: Support rmod for RHS subclasses of str in % string formatting operations by mjpieters · Pull Request #51 · python/cpython · GitHub

When you use '%s' % SubClassOfStr(), where SubClassOfStr.__rmod__ exists, the reverse operation is ignored as normally such string formatting operations use the PyUnicode_Format() fast path. This patch tests for subclasses of str first and picks the slow path in that case.

Fixes bpo-28598.

…rations. When you use `'%s' % SubClassOfStr()`, where `SubClassOfStr.__rmod__` exists, the reverse operation is ignored as normally such string formatting operations use the `PyUnicode_Format()` fast path. This patch tests for subclasses of `str` first and picks the slow path in that case. Fixes issue28598.

Open question: Should this patch be backported to 3.6 and 3.5? It's a bug fix, not a new feature.

Should this patch be backported to 3.6 and 3.5?

Yes, it should be backported if it's a bug (I haven't investigated myself yet.)

I'm not sure if issues are linked automatically yet.

We don't use issueNNNN anymore. The correct way to link PRs to bugs.p.o is bpo-NNNN.

We don't use issueNNNN anymore. The correct way to link PRs to bugs.p.o is bpo-NNNN.

Ta, also for the title change! Updated the 'fixes' line too.

In general LGTM except few minor details.

And I'm not sure about the style of commit messages now. Should it include issue number at the first line? Should it contain "Patch by YYY." (now the author is specified in metadata)?

Too many negations.

I would expand the expression as PyUnicode_CheckExact(dividend) && (!PyUnicode_Check(divisor) || PyUnicode_CheckExact(divisor)).

Add "Patch by Martijn Pieters."

Codecov Report

Merging #51 into master will decrease coverage by -0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #51      +/-   ##
==========================================
- Coverage   82.37%   82.37%   -0.01%     
==========================================
  Files        1427     1427              
  Lines      350948   350953       +5     
==========================================
- Hits       289099   289097       -2     
- Misses      61849    61856       +7

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Should this really be backported? It seems like a change in semantics more than a bugfix.

@brettcannon This is definitely a bug, not a change in semantics. From the object.__rmod__ documentation:

Note: If the right operand’s type is a subclass of the left operand’s type and that subclass provides the reflected method for the operation, this method will be called before the left operand’s non-reflected method. This behavior allows subclasses to override their ancestors’ operations.

str % subclass_of_str doesn't follow this behavior, and str is the only type that doesn't (everything else goes through the PyNumber_Remainder() slow path). This patch fixes that bug.

See #51

Allow miss-islington to merge the PR if all of these conditions met: - All CI passed - At least one core dev approved - PR is made by miss-islington

Back port latest changes to importlib.resources Closes python#51 See merge request python-devs/importlib_resources!55

…ython#51) * feat: store bb_test flag in frame to reload during resume * feat: bigger CACHE entries for everything, CACHE for JUMP_BACKWARD * nit: increase overallocate factor even more * feat: remove bb_flag/bb_test and use only the frame's

Fix bad merge

the-knights-who-say-ni added the CLA signed label Feb 12, 2017

berkerpeksag changed the title Support __rmod__ for RHS subclasses of str in % string formatting operations bpo-28598: Support __rmod__ for RHS subclasses of str in % string formatting operations Feb 12, 2017

serhiy-storchaka reviewed Feb 12, 2017

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berkerpeksag added backport to 3.5 labels Feb 12, 2017

Address review comments; reduce negations and credit patch

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serhiy-storchaka approved these changes Feb 13, 2017

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serhiy-storchaka added the type-bug An unexpected behavior, bug, or error label Feb 18, 2017

methane mentioned this pull request Feb 21, 2017

.gitattribute -> .gitattributes #213

Merged

Merge branch 'master' into issue28598_str_rmod_fix

f596f01

serhiy-storchaka merged commit d7e6433 into python:master Feb 23, 2017

zhangyangyu added the needs backport to 2.7 label Mar 1, 2017

zhangyangyu mentioned this pull request Mar 1, 2017

[2.7] bpo-28598: Support __rmod__ for RHS subclasses of str in % string formatting operations #366

Merged

Mariatta removed needs backport to 2.7 labels Mar 1, 2017

mjpieters mentioned this pull request Mar 1, 2017

[backport to 2.7] bpo-28598: Support __rmod__ for RHS subclasses of str in % string formatting operations #382

Closed

mjpieters deleted the issue28598_str_rmod_fix branch March 1, 2017 16:55

colesbury referenced this pull request in colesbury/nogil Oct 6, 2021

Add a lock around dtoa mult5 code

ec46739

See #51

tendermonster mentioned this pull request Oct 19, 2022

Multiprocessing returns Array, RawArray of wrong length python 3.10.4 #98447

Closed

jaraco pushed a commit that referenced this pull request Dec 2, 2022

Merge the PR with one core dev approval and CI passed. (GH-51 )

69f93c6

Allow miss-islington to merge the PR if all of these conditions met: - All CI passed - At least one core dev approved - PR is made by miss-islington

jaraco pushed a commit to jaraco/cpython that referenced this pull request Feb 17, 2023

Merge branch 'issue51' into 'master'

bd5afac

Back port latest changes to importlib.resources Closes python#51 See merge request python-devs/importlib_resources!55

mgmacias95 pushed a commit to mgmacias95/cpython that referenced this pull request Mar 24, 2023

Merge pull request python#51 from isidentical/more-simplifications

b41a3b8

gvanrossum mentioned this pull request Aug 22, 2023

heap-use-after-free in _PyFunction_LookupByVersion #108253

Closed

LinanV mentioned this pull request Oct 23, 2023

Objects/typeobject.c: No such file or directory. #111203

Closed

kcatss mentioned this pull request Feb 20, 2024

Use After Free at _heapreplace_max #115706

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ngoldbaum mentioned this pull request Sep 23, 2024

Crash running PyO3 tests with --test-threads=1000 #124375

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This was referenced Feb 11, 2025

segmentfault when pip installing setuptools #129992

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segmentfault when pip installing setuptools #129993

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sergey-miryanov mentioned this pull request Dec 18, 2025

Observed memory leak in ssl library: Python 3.14 GC issue #142516

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DinoV added a commit to DinoV/cpython that referenced this pull request Feb 11, 2026

Merge pull request python#51 from DinoV/fix_merge

80b3925

Fix bad merge

ngoldbaum mentioned this pull request Mar 6, 2026

Remove deprecated and undocumented function ctypes.SetPointerType #133866

Closed

-                              PyNumber_Remainder(dividend, divisor);
+                          PyObject *res;
+                          if (PyUnicode_CheckExact(dividend) && !(
+                                PyUnicode_Check(divisor) && !PyUnicode_CheckExact(divisor))) {

bpo-28598: Support rmod for RHS subclasses of str in % string formatting operations by mjpieters · Pull Request #51 · python/cpython · GitHub

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bpo-28598: Support rmod for RHS subclasses of str in % string formatting operations - #51

bpo-28598: Support rmod for RHS subclasses of str in % string formatting operations#51
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               Core and Builtins
               -----------------
+              - Issue #28598: Support __rmod__ for subclasses of str being called before str.__mod__.

bpo-28598: Support __rmod__ for RHS subclasses of str in % string formatting operations by mjpieters · Pull Request #51 · python/cpython · GitHub

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bpo-28598: Support __rmod__ for RHS subclasses of str in % string formatting operations#51serhiy-storchaka merged 3 commits intopython:masterpython/cpython:masterfrom mjpieters:issue28598_str_rmod_fixCopy head branch name to clipboard

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bpo-28598: Support rmod for RHS subclasses of str in % string formatting operations by mjpieters · Pull Request #51 · python/cpython · GitHub

bpo-28598: Support rmod for RHS subclasses of str in % string formatting operations - #51

bpo-28598: Support rmod for RHS subclasses of str in % string formatting operations#51
serhiy-storchaka merged 3 commits into
python:masterfrom
mjpieters:issue28598_str_rmod_fix

mjpieters commented Feb 12, 2017 •
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