bpo-28598: Support __rmod__ for RHS subclasses of str in % string formatting operations #51
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…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.
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Open question: Should this patch be backported to 3.6 and 3.5? It's a bug fix, not a new feature. |
Yes, it should be backported if it's a bug (I haven't investigated myself yet.)
We don't use |
Ta, also for the title change! Updated the 'fixes' line too. |
Python/ceval.c
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| PyNumber_Remainder(dividend, divisor); | ||
| PyObject *res; | ||
| if (PyUnicode_CheckExact(dividend) && !( | ||
| PyUnicode_Check(divisor) && !PyUnicode_CheckExact(divisor))) { |
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Too many negations.
I would expand the expression as PyUnicode_CheckExact(dividend) && (!PyUnicode_Check(divisor) || PyUnicode_CheckExact(divisor)).
Misc/NEWS
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| @@ -10,6 +10,8 @@ What's New in Python 3.7.0 alpha 1? | |||
| Core and Builtins | |||
| ----------------- | |||
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| - Issue #28598: Support __rmod__ for subclasses of str being called before str.__mod__. | |||
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Add "Patch by Martijn Pieters."
Codecov Report
@@ Coverage Diff @@
## master #51 +/- ##
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- Coverage 82.37% 82.37% -0.01%
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Files 1427 1427
Lines 350948 350953 +5
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- Hits 289099 289097 -2
- Misses 61849 61856 +7Continue to review full report at Codecov.
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Should this really be backported? It seems like a change in semantics more than a bugfix. |
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@brettcannon This is definitely a bug, not a change in semantics. From the
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When you use
'%s' % SubClassOfStr(), whereSubClassOfStr.__rmod__exists, the reverse operation is ignored as normally such string formatting operations use thePyUnicode_Format()fast path. This patch tests for subclasses ofstrfirst and picks the slow path in that case.Fixes bpo-28598.