From 37551c9cef307ca3172c60b28c7de9db921808ad Mon Sep 17 00:00:00 2001
From: Inada Naoki <songofacandy@gmail.com>
Date: Sat, 29 Jul 2023 15:37:23 +0900
Subject: [PATCH] gh-107369: optimize textwrap.indent() (#107374)

---
 Doc/whatsnew/3.13.rst                          |  3 ++-
 Lib/textwrap.py                                | 18 ++++++++++++------
 ...3-07-28-14-56-35.gh-issue-107369.bvTq8F.rst |  2 ++
 3 files changed, 16 insertions(+), 7 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2023-07-28-14-56-35.gh-issue-107369.bvTq8F.rst

diff --git a/Doc/whatsnew/3.13.rst b/Doc/whatsnew/3.13.rst
index 7cad5d1ec02..e20832a3a4c 100644
--- a/Doc/whatsnew/3.13.rst
+++ b/Doc/whatsnew/3.13.rst
@@ -150,7 +150,8 @@ typing
 Optimizations
 =============
 
-
+* :func:`textwrap.indent` is now ~30% faster than before for large input.
+  (Contributed by Inada Naoki in :gh:`107369`.)
 
 
 Deprecated
diff --git a/Lib/textwrap.py b/Lib/textwrap.py
index 98bedd27ea3..7ca393d1c37 100644
--- a/Lib/textwrap.py
+++ b/Lib/textwrap.py
@@ -476,13 +476,19 @@ def indent(text, prefix, predicate=None):
     consist solely of whitespace characters.
     """
     if predicate is None:
-        def predicate(line):
-            return line.strip()
+        # str.splitlines(True) doesn't produce empty string.
+        #  ''.splitlines(True) => []
+        #  'foo\n'.splitlines(True) => ['foo\n']
+        # So we can use just `not s.isspace()` here.
+        predicate = lambda s: not s.isspace()
 
-    def prefixed_lines():
-        for line in text.splitlines(True):
-            yield (prefix + line if predicate(line) else line)
-    return ''.join(prefixed_lines())
+    prefixed_lines = []
+    for line in text.splitlines(True):
+        if predicate(line):
+            prefixed_lines.append(prefix)
+        prefixed_lines.append(line)
+
+    return ''.join(prefixed_lines)
 
 
 if __name__ == "__main__":
diff --git a/Misc/NEWS.d/next/Library/2023-07-28-14-56-35.gh-issue-107369.bvTq8F.rst b/Misc/NEWS.d/next/Library/2023-07-28-14-56-35.gh-issue-107369.bvTq8F.rst
new file mode 100644
index 00000000000..76aeab65e90
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-07-28-14-56-35.gh-issue-107369.bvTq8F.rst
@@ -0,0 +1,2 @@
+Optimize :func:`textwrap.indent`. It is ~30% faster for large input. Patch
+by Inada Naoki.