From 1ef5f557c3512b7f6ddfb7ddc6fa9507573713fe Mon Sep 17 00:00:00 2001 From: Martijn Pieters Date: Sun, 12 Feb 2017 15:10:50 +0000 Subject: [PATCH 1/2] Support __rmod__ for RHS subclasses of str in % string formatting operations. 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. --- Lib/test/test_unicode.py | 9 +++++++++ Misc/NEWS | 2 ++ Python/ceval.c | 12 +++++++++--- 3 files changed, 20 insertions(+), 3 deletions(-) diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py index b1f7c8966aa11c..f70504c11afdc0 100644 --- a/Lib/test/test_unicode.py +++ b/Lib/test/test_unicode.py @@ -1448,6 +1448,15 @@ def test_formatting_huge_precision(self): with self.assertRaises(ValueError): result = format_string % 2.34 + def test_issue28598_strsubclass_rhs(self): + # A subclass of str with an __rmod__ method should be able to hook + # into the % operator + class SubclassedStr(str): + def __rmod__(self, other): + return 'Success, self.__rmod__({!r}) was called'.format(other) + self.assertEqual('lhs %% %r' % SubclassedStr('rhs'), + "Success, self.__rmod__('lhs %% %r') was called") + @support.cpython_only def test_formatting_huge_precision_c_limits(self): from _testcapi import INT_MAX diff --git a/Misc/NEWS b/Misc/NEWS index eb870b7d48b76b..0038a126505fde 100644 --- a/Misc/NEWS +++ b/Misc/NEWS @@ -10,6 +10,8 @@ What's New in Python 3.7.0 alpha 1? Core and Builtins ----------------- +- Issue #28598: Support __rmod__ for subclasses of str being called before str.__mod__. + - bpo-29438: Fixed use-after-free problem in key sharing dict. - Issue #29319: Prevent RunMainFromImporter overwriting sys.path[0]. diff --git a/Python/ceval.c b/Python/ceval.c index 58007793bb9de0..871e14a6e8caca 100644 --- a/Python/ceval.c +++ b/Python/ceval.c @@ -1355,9 +1355,15 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag) TARGET(BINARY_MODULO) { PyObject *divisor = POP(); PyObject *dividend = TOP(); - PyObject *res = PyUnicode_CheckExact(dividend) ? - PyUnicode_Format(dividend, divisor) : - PyNumber_Remainder(dividend, divisor); + PyObject *res; + if (PyUnicode_CheckExact(dividend) && !( + PyUnicode_Check(divisor) && !PyUnicode_CheckExact(divisor))) { + // fast path; string formatting, but not if the RHS is a str subclass + // (see issue28598) + res = PyUnicode_Format(dividend, divisor); + } else { + res = PyNumber_Remainder(dividend, divisor); + } Py_DECREF(divisor); Py_DECREF(dividend); SET_TOP(res); From 7b19b0265145eb3d7017569a2522cbd14a9f6072 Mon Sep 17 00:00:00 2001 From: Martijn Pieters Date: Sun, 12 Feb 2017 17:34:41 +0000 Subject: [PATCH 2/2] Address review comments; reduce negations and credit patch --- Misc/NEWS | 3 ++- Python/ceval.c | 4 ++-- 2 files changed, 4 insertions(+), 3 deletions(-) diff --git a/Misc/NEWS b/Misc/NEWS index 0038a126505fde..964ce01c38882e 100644 --- a/Misc/NEWS +++ b/Misc/NEWS @@ -10,7 +10,8 @@ What's New in Python 3.7.0 alpha 1? Core and Builtins ----------------- -- Issue #28598: Support __rmod__ for subclasses of str being called before str.__mod__. +- Issue #28598: Support __rmod__ for subclasses of str being called before + str.__mod__. Patch by Martijn Pieters. - bpo-29438: Fixed use-after-free problem in key sharing dict. diff --git a/Python/ceval.c b/Python/ceval.c index 871e14a6e8caca..b6347e436e0ea1 100644 --- a/Python/ceval.c +++ b/Python/ceval.c @@ -1356,8 +1356,8 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag) PyObject *divisor = POP(); PyObject *dividend = TOP(); PyObject *res; - if (PyUnicode_CheckExact(dividend) && !( - PyUnicode_Check(divisor) && !PyUnicode_CheckExact(divisor))) { + if (PyUnicode_CheckExact(dividend) && ( + !PyUnicode_Check(divisor) || PyUnicode_CheckExact(divisor))) { // fast path; string formatting, but not if the RHS is a str subclass // (see issue28598) res = PyUnicode_Format(dividend, divisor);