bpo-28528: Fix pdb.checkline() attribute error when 'curframe' is None. (#25438)

 Co-authored-by: Thomas Kluyver <takowl@gmail.com>

Author: Erlend Egeberg Aasland

Lib/pdb.py

@@ -752,7 +752,8 @@ def checkline(self, filename, lineno):
  """
  # 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')

Lib/test/test_pdb.py

@@ -9,6 +9,7 @@
 import unittest
 import subprocess
 import textwrap
+import linecache
 
 from contextlib import ExitStack
 from io import StringIO
@@ -1807,10 +1808,47 @@ def test_issue42383(self):
  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)

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`.