bpo-28528: Harden pdb.checkline()

Test case C&P from T. Kluyver's patch.

Co-written-by: Thomas Kluyver <[email protected]>

Author: Erlend E. Aasland

Lib/pdb.py

@@ -752,7 +752,10 @@ 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
+        try:
+            globs = self.curframe.f_globals
+        except AttributeError:
+            globs = None
         line = linecache.getline(filename, lineno, globs)
         if not line:
             self.message('End of file')

Lib/test/test_pdb.py

@@ -1806,6 +1806,14 @@ def test_issue42383(self):
             expected = '(Pdb) The correct file was executed'
             self.assertEqual(stdout.split('\n')[6].rstrip('\r'), expected)
 
+    def test_issue28528(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)
+        db.reset()
+        self.assertEqual(db.checkline(os_helper.TESTFN, 1), 1)
+
 
 def load_tests(*args):
     from test import test_pdb