From 8563a7052ccd98e6a381d361664ce567afd5eb6e Mon Sep 17 00:00:00 2001
From: Erlend Egeberg Aasland <erlend.aasland@innova.no>
Date: Wed, 12 May 2021 01:26:30 +0200
Subject: bpo-28528: Fix pdb.checkline() attribute error when 'curframe' is
 None. (#25438)

Co-authored-by: Thomas Kluyver <takowl@gmail.com>
---
 Lib/pdb.py                                         |  3 +-
 Lib/test/test_pdb.py                               | 38 ++++++++++++++++++++++
 .../2021-04-29-00-48-00.bpo-28528.JLAVWj.rst       |  2 ++
 3 files changed, 42 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2021-04-29-00-48-00.bpo-28528.JLAVWj.rst

diff --git a/Lib/pdb.py b/Lib/pdb.py
index 98dc975..a888a0a 100755
--- a/Lib/pdb.py
+++ b/Lib/pdb.py
@@ -752,7 +752,8 @@ class Pdb(bdb.Bdb, cmd.Cmd):
         """
         # this method should be callable before starting debugging, so default
         # to "no globals" if there is no current frame
-        globs = self.curframe.f_globals if hasattr(self, 'curframe') else None
+        frame = getattr(self, 'curframe', None)
+        globs = frame.f_globals if frame else None
         line = linecache.getline(filename, lineno, globs)
         if not line:
             self.message('End of file')
diff --git a/Lib/test/test_pdb.py b/Lib/test/test_pdb.py
index 870eab4..cd096e7 100644
--- a/Lib/test/test_pdb.py
+++ b/Lib/test/test_pdb.py
@@ -9,6 +9,7 @@ import codecs
 import unittest
 import subprocess
 import textwrap
+import linecache
 
 from contextlib import ExitStack
 from io import StringIO
@@ -1807,10 +1808,47 @@ def bœr():
             self.assertEqual(stdout.split('\n')[6].rstrip('\r'), expected)
 
 
+class ChecklineTests(unittest.TestCase):
+    def setUp(self):
+        linecache.clearcache()  # Pdb.checkline() uses linecache.getline()
+
+    def tearDown(self):
+        os_helper.unlink(os_helper.TESTFN)
+
+    def test_checkline_before_debugging(self):
+        with open(os_helper.TESTFN, "w") as f:
+            f.write("print(123)")
+        db = pdb.Pdb()
+        self.assertEqual(db.checkline(os_helper.TESTFN, 1), 1)
+
+    def test_checkline_after_reset(self):
+        with open(os_helper.TESTFN, "w") as f:
+            f.write("print(123)")
+        db = pdb.Pdb()
+        db.reset()
+        self.assertEqual(db.checkline(os_helper.TESTFN, 1), 1)
+
+    def test_checkline_is_not_executable(self):
+        with open(os_helper.TESTFN, "w") as f:
+            # Test for comments, docstrings and empty lines
+            s = textwrap.dedent("""
+                # Comment
+                \"\"\" docstring \"\"\"
+                ''' docstring '''
+
+            """)
+            f.write(s)
+        db = pdb.Pdb()
+        num_lines = len(s.splitlines()) + 2  # Test for EOF
+        for lineno in range(num_lines):
+            self.assertFalse(db.checkline(os_helper.TESTFN, lineno))
+
+
 def load_tests(*args):
     from test import test_pdb
     suites = [
         unittest.makeSuite(PdbTestCase),
+        unittest.makeSuite(ChecklineTests),
         doctest.DocTestSuite(test_pdb)
     ]
     return unittest.TestSuite(suites)
diff --git a/Misc/NEWS.d/next/Library/2021-04-29-00-48-00.bpo-28528.JLAVWj.rst b/Misc/NEWS.d/next/Library/2021-04-29-00-48-00.bpo-28528.JLAVWj.rst
new file mode 100644
index 0000000..97731ad
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-04-29-00-48-00.bpo-28528.JLAVWj.rst
@@ -0,0 +1,2 @@
+Fix a bug in :mod:`pdb` where :meth:`~pdb.Pdb.checkline` raises
+:exc:`AttributeError` if it is called after :meth:`~pdb.Pdb.reset`.
-- 
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