https://github.com/python/cpython/commit/c79e18a8e5ff4fda1a3d9201e65b0c6048b56b68
commit: c79e18a8e5ff4fda1a3d9201e65b0c6048b56b68
branch: main
author: Bernát Gábor <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2026-06-02T10:45:30+03:00
summary:
gh-150717: Avoid mark-array allocation for groupless regex patterns (GH-150719)
state_init() always did PyMem_New(state->mark, groups*2), which for a
pattern with no capturing groups is PyMem_Malloc(0) -- a real allocation
(plus matching free) on every match/search/fullmatch call, for an array
that is never read: groupless patterns emit no MARK opcodes and group 0's
span is taken from state->start/ptr.
Guard the allocation with `if (pattern->groups)`. state->mark stays NULL
(set by the preceding memset), and both the error path and state_fini
already PyMem_Free(NULL) safely.
files:
A Misc/NEWS.d/next/Library/2026-06-01-08-12-34.gh-issue-150717.LVRJXH.rst
M Modules/_sre/sre.c
diff --git
a/Misc/NEWS.d/next/Library/2026-06-01-08-12-34.gh-issue-150717.LVRJXH.rst
b/Misc/NEWS.d/next/Library/2026-06-01-08-12-34.gh-issue-150717.LVRJXH.rst
new file mode 100644
index 000000000000000..da7171fcc72ce41
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-06-01-08-12-34.gh-issue-150717.LVRJXH.rst
@@ -0,0 +1,2 @@
+Avoid an unnecessary per-call memory allocation when matching :mod:`re`
+patterns that have no capturing groups. Patch by Bernát Gábor.
diff --git a/Modules/_sre/sre.c b/Modules/_sre/sre.c
index 7a07ed1d7aca20c..058a03148c823fb 100644
--- a/Modules/_sre/sre.c
+++ b/Modules/_sre/sre.c
@@ -548,10 +548,16 @@ state_init(SRE_STATE* state, PatternObject* pattern,
PyObject* string,
memset(state, 0, sizeof(SRE_STATE));
- state->mark = PyMem_New(const void *, pattern->groups * 2);
- if (!state->mark) {
- PyErr_NoMemory();
- goto err;
+ /* Patterns with no capturing groups never emit MARK opcodes and never
+ read state->mark (group 0's span comes from state->start/ptr), so skip
+ the allocation entirely -- state->mark stays NULL, which both the err
+ path and state_fini already free safely. */
+ if (pattern->groups) {
+ state->mark = PyMem_New(const void *, pattern->groups * 2);
+ if (!state->mark) {
+ PyErr_NoMemory();
+ goto err;
+ }
}
state->lastmark = -1;
state->lastindex = -1;
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