[Python-checkins] bpo-37723: Fix performance regression on regular expression parsing. (GH-15030)

[Miss Islington (bot)]

https://github.com/python/cpython/commit/33b700ba8cbb128519442eeed8c8747ff73f4524
commit: 33b700ba8cbb128519442eeed8c8747ff73f4524
branch: 3.7
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: GitHub <noreply at github.com>
date: 2019-07-31T13:22:19-07:00
summary:

bpo-37723: Fix performance regression on regular expression parsing. (GH-15030)


Improve performance of sre_parse._uniq function.
(cherry picked from commit 9f55551f3df238e58315e724e50cb0d574d75b94)

Co-authored-by: yannvgn <hi at yannvgn.io>

files:
A Misc/NEWS.d/next/Library/2019-07-31-16-49-01.bpo-37723.zq6tw8.rst
M Lib/sre_parse.py
M Misc/ACKS

diff --git a/Lib/sre_parse.py b/Lib/sre_parse.py
index a53735b07ded..cb2c4c3281c9 100644
--- a/Lib/sre_parse.py
+++ b/Lib/sre_parse.py
@@ -406,13 +406,7 @@ def _escape(source, escape, state):
     raise source.error("bad escape %s" % escape, len(escape))
 
 def _uniq(items):
-    if len(set(items)) == len(items):
-        return items
-    newitems = []
-    for item in items:
-        if item not in newitems:
-            newitems.append(item)
-    return newitems
+    return list(dict.fromkeys(items))
 
 def _parse_sub(source, state, verbose, nested):
     # parse an alternation: a|b|c
diff --git a/Misc/ACKS b/Misc/ACKS
index 1b54d7ef7f18..29b6690f2174 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1672,6 +1672,7 @@ Michael Urman
 Hector Urtubia
 Lukas Vacek
 Ville Vainio
+Yann Vaginay
 Andi Vajda
 Case Van Horsen
 John Mark Vandenberg
diff --git a/Misc/NEWS.d/next/Library/2019-07-31-16-49-01.bpo-37723.zq6tw8.rst b/Misc/NEWS.d/next/Library/2019-07-31-16-49-01.bpo-37723.zq6tw8.rst
new file mode 100644
index 000000000000..65507bd0dc91
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-07-31-16-49-01.bpo-37723.zq6tw8.rst
@@ -0,0 +1,2 @@
+Fix performance regression on regular expression parsing with huge
+character sets. Patch by Yann Vaginay.
\ No newline at end of file