https://github.com/python/cpython/commit/6107e915526f9bf162452e98ce043c2df0db712c commit: 6107e915526f9bf162452e98ce043c2df0db712c branch: 3.14 author: Miss Islington (bot) <[email protected]> committer: warsaw <[email protected]> date: 2026-07-08T14:43:54-07:00 summary:
[3.14] gh-153056: Fix a data race compiling the string.Template pattern in free-threading builds (GH-153057) (#153303) gh-153056: Fix a data race compiling the string.Template pattern in free-threading builds (GH-153057) * gh-153056: Fix a data race compiling the string.Template pattern in free-threading builds Template compiles its substitution pattern lazily and caches it on the class. On the free-threaded build two concurrent first uses could race: a thread that observed the pattern another thread had just compiled would try to recompile it, and re.compile() rejects flags on an already-compiled pattern, raising a spurious ValueError. Return the already-compiled pattern instead. As a side effect, a subclass that supplies an already-compiled pattern now works too; previously it raised the same ValueError at class definition. * Trim test comments and NEWS wording * Document that the pattern attribute accepts a string or a compiled regex * Comment the three states of pattern and note the documented-behavior fix in NEWS * Update Doc/library/string.rst --------- (cherry picked from commit 45729033bff28f8abc36c42e802cb2853c205737) Co-authored-by: tonghuaroot (童话) <[email protected]> Co-authored-by: Barry Warsaw <[email protected]> files: A Lib/test/test_free_threading/test_string_template_race.py A Misc/NEWS.d/next/Library/2026-07-05-12-00-00.gh-issue-153056.tMpLat.rst M Doc/library/string.rst M Lib/string/__init__.py M Lib/test/test_string/test_string.py diff --git a/Doc/library/string.rst b/Doc/library/string.rst index be968a3c53d8430..f1abed91d20ed51 100644 --- a/Doc/library/string.rst +++ b/Doc/library/string.rst @@ -971,7 +971,8 @@ attributes: Alternatively, you can provide the entire regular expression pattern by overriding the class attribute *pattern*. If you do this, the value must be a -regular expression object with four named capturing groups. The capturing +regular expression pattern string, or a compiled regular expression +object, with four named capturing groups. The capturing groups correspond to the rules given above, along with the invalid placeholder rule: diff --git a/Lib/string/__init__.py b/Lib/string/__init__.py index eab5067c9b133ea..b2c369ef9d1f76c 100644 --- a/Lib/string/__init__.py +++ b/Lib/string/__init__.py @@ -83,7 +83,14 @@ def __init_subclass__(cls): def _compile_pattern(cls): import re # deferred import, for performance + # `pattern` may be the `_TemplatePattern` sentinel (not yet compiled), an + # already-compiled regular expression object (as documented), or a string + # regular expression. An already-compiled object is returned as-is; the + # other two are compiled and cached back on the class. pattern = cls.__dict__.get('pattern', _TemplatePattern) + if isinstance(pattern, re.Pattern): + # re.compile() rejects flags on an already-compiled pattern. + return pattern if pattern is _TemplatePattern: delim = re.escape(cls.delimiter) id = cls.idpattern diff --git a/Lib/test/test_free_threading/test_string_template_race.py b/Lib/test/test_free_threading/test_string_template_race.py new file mode 100644 index 000000000000000..dc4b4e9f18d2863 --- /dev/null +++ b/Lib/test/test_free_threading/test_string_template_race.py @@ -0,0 +1,35 @@ +import string +import unittest +from string import Template + +from test.support import threading_helper + + +@threading_helper.requires_working_threading() +class TestTemplateCompileRace(unittest.TestCase): + def test_concurrent_first_use(self): + # Racing the lazy pattern compile must not raise a spurious ValueError + # from recompiling an already-compiled pattern. A throwaway subclass, + # re-armed to the sentinel each round, keeps string.Template unmutated + # (subclasses precompile eagerly in __init_subclass__). + uncompiled = string._TemplatePattern + errors = [] + + def use_template(cls): + try: + cls("$x and ${y}").substitute(x=1, y=2) + except Exception as e: + errors.append(e) + + for _ in range(20): + class T(Template): + pass + T.pattern = uncompiled + T.flags = None + threading_helper.run_concurrently(use_template, nthreads=10, args=(T,)) + + self.assertEqual(errors, [], msg=f"unexpected errors: {errors}") + + +if __name__ == "__main__": + unittest.main() diff --git a/Lib/test/test_string/test_string.py b/Lib/test/test_string/test_string.py index 5394fe4e12cd41c..350784a9f00817b 100644 --- a/Lib/test/test_string/test_string.py +++ b/Lib/test/test_string/test_string.py @@ -299,6 +299,20 @@ def test_SafeTemplate(self): eq(s.safe_substitute(dict(who='tim', what='ham', meal='dinner')), 'tim likes ham for dinner') + def test_precompiled_pattern(self): + # A subclass may supply an already-compiled pattern; it must be reused, + # not recompiled (re.compile() rejects flags on a compiled pattern). + import re + compiled = re.compile( + r'\$(?:(?P<escaped>\$)|(?P<named>[a-z]+)|' + r'\{(?P<braced>[a-z]+)\}|(?P<invalid>))') + class MyTemplate(Template): + pattern = compiled + self.assertIs(MyTemplate.pattern, compiled) + self.assertEqual( + MyTemplate('$who likes $what').substitute(who='tim', what='ham'), + 'tim likes ham') + def test_invalid_placeholders(self): raises = self.assertRaises s = Template('$who likes $') diff --git a/Misc/NEWS.d/next/Library/2026-07-05-12-00-00.gh-issue-153056.tMpLat.rst b/Misc/NEWS.d/next/Library/2026-07-05-12-00-00.gh-issue-153056.tMpLat.rst new file mode 100644 index 000000000000000..a2bc89f25a53c19 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2026-07-05-12-00-00.gh-issue-153056.tMpLat.rst @@ -0,0 +1,4 @@ +Fix :class:`string.Template` raising a spurious :exc:`ValueError` when the +*pattern* attribute is a compiled regular expression object, which the +documentation allows. On the free-threaded build this also occurred as a data +race on the first concurrent use. _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
