From e7c5f60efc149dda3d3592fa2001f4583b128512 Mon Sep 17 00:00:00 2001
From: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
Date: Sat, 19 Apr 2025 16:18:03 +0100
Subject: [PATCH] gh-130167: Improve the error case for ``textwrap.dedent``
 (#132666)

---
 Lib/test/test_textwrap.py | 7 +++++++
 Lib/textwrap.py           | 9 +++++----
 Misc/NEWS.d/3.14.0a7.rst  | 2 +-
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/Lib/test/test_textwrap.py b/Lib/test/test_textwrap.py
index 77366988b57..cbd383ea4e2 100644
--- a/Lib/test/test_textwrap.py
+++ b/Lib/test/test_textwrap.py
@@ -765,6 +765,13 @@ some (including a hanging indent).'''
 # of IndentTestCase!
 class DedentTestCase(unittest.TestCase):
 
+    def test_type_error(self):
+        with self.assertRaisesRegex(TypeError, "expected str object, not"):
+            dedent(0)
+
+        with self.assertRaisesRegex(TypeError, "expected str object, not"):
+            dedent(b'')
+
     def assertUnchanged(self, text):
         """assert that dedent() has no effect on 'text'"""
         self.assertEqual(text, dedent(text))
diff --git a/Lib/textwrap.py b/Lib/textwrap.py
index bac98c99e41..00465f67d09 100644
--- a/Lib/textwrap.py
+++ b/Lib/textwrap.py
@@ -426,10 +426,11 @@ def dedent(text):
 
     Entirely blank lines are normalized to a newline character.
     """
-    if not text:
-        return text
-
-    lines = text.split('\n')
+    try:
+        lines = text.split('\n')
+    except (AttributeError, TypeError):
+        msg = f'expected str object, not {type(text).__qualname__!r}'
+        raise TypeError(msg) from None
 
     # Get length of leading whitespace, inspired by ``os.path.commonprefix()``.
     non_blank_lines = [l for l in lines if l and not l.isspace()]
diff --git a/Misc/NEWS.d/3.14.0a7.rst b/Misc/NEWS.d/3.14.0a7.rst
index 900cde10641..35b96d33da4 100644
--- a/Misc/NEWS.d/3.14.0a7.rst
+++ b/Misc/NEWS.d/3.14.0a7.rst
@@ -288,7 +288,7 @@ Improve the import time of the :mod:`ast` module by extracting the
 .. nonce: 8M-HVz
 .. section: Library
 
-Improved performance of :func:`textwrap.dedent` by an average of ~1.3x.
+Improved performance of :func:`textwrap.indent` by an average of ~1.3x.
 Patch by Adam Turner.
 
 ..