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bpo-42885: Optimize search for regular expressions starting with "\A" or "^" #32021

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Merged
serhiy-storchaka merged 5 commits into from
Mar 22, 2022
Merged

bpo-42885: Optimize search for regular expressions starting with "\A" or "^" #32021

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5f66afe
bpo-42885: Optimize search for regular expressions starting with "\A"…
serhiy-storchaka Mar 21, 2022
9345412
Merge branch 'main' into re-search-at-beginning
serhiy-storchaka Mar 21, 2022
1af3c58
Test timing.
serhiy-storchaka Mar 22, 2022
25f9e25
Merge branch 'main' into re-search-at-beginning
serhiy-storchaka Mar 22, 2022
c7c8c07
Merge branch 'main' into re-search-at-beginning
serhiy-storchaka Mar 22, 2022
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15 changes: 15 additions & 0 deletions Lib/test/test_re.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
import re
import sre_compile
import string
import time
import unittest
import warnings
from re import Scanner
Expand Down Expand Up @@ -2038,6 +2039,20 @@ def test_bug_40736(self):
with self.assertRaisesRegex(TypeError, "got 'type'"):
re.search("x*", type)

def test_search_anchor_at_beginning(self):
s = 'x'*10**7
start = time.perf_counter()
for p in r'\Ay', r'^y':
self.assertIsNone(re.search(p, s))
self.assertEqual(re.split(p, s), [s])
self.assertEqual(re.findall(p, s), [])
self.assertEqual(list(re.finditer(p, s)), [])
self.assertEqual(re.sub(p, '', s), s)
t = time.perf_counter() - start
# Without optimization it takes 1 second on my computer.
# With optimization -- 0.0003 seconds.
self.assertLess(t, 0.1)

def test_possessive_quantifiers(self):
"""Test Possessive Quantifiers
Test quantifiers of the form @+ for some repetition operator @,
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2022-03-21-08-32-19.bpo-42885.LCnTTp.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Optimize :func:`re.search`, :func:`re.split`, :func:`re.findall`,
:func:`re.finditer` and :func:`re.sub` for regular expressions starting with
``\A`` or ``^``.
7 changes: 7 additions & 0 deletions Modules/sre_lib.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1693,6 +1693,13 @@ SRE(search)(SRE_STATE* state, SRE_CODE* pattern)
state->start = state->ptr = ptr;
status = SRE(match)(state, pattern, 1);
state->must_advance = 0;
if (status == 0 && pattern[0] == SRE_OP_AT &&
(pattern[1] == SRE_AT_BEGINNING ||
pattern[1] == SRE_AT_BEGINNING_STRING))
{
state->start = state->ptr = ptr = end;
return 0;
}
while (status == 0 && ptr < end) {
ptr++;
RESET_CAPTURE_GROUP();
Expand Down