Issue #20766: Fix references leaked by pdb in the handling of SIGINT handlers.

Lib/pdb.py

@@ -134,6 +134,8 @@ line_prefix = '\n-> '   # Probably a better default
 
 class Pdb(bdb.Bdb, cmd.Cmd):
 
+    _previous_sigint_handler = None
+
     def __init__(self, completekey='tab', stdin=None, stdout=None, skip=None,
                  nosigint=False):
         bdb.Bdb.__init__(self, skip=skip)
@@ -187,8 +189,6 @@ class Pdb(bdb.Bdb, cmd.Cmd):
         self.message("\nProgram interrupted. (Use 'cont' to resume).")
         self.set_step()
         self.set_trace(frame)
-        # restore previous signal handler
-        signal.signal(signal.SIGINT, self._previous_sigint_handler)
 
     def reset(self):
         bdb.Bdb.reset(self)
@@ -337,6 +337,10 @@ class Pdb(bdb.Bdb, cmd.Cmd):
                                  (expr, newvalue, oldvalue))
 
     def interaction(self, frame, traceback):
+        # Restore the previous signal handler at the Pdb prompt.
+        if Pdb._previous_sigint_handler:
+            signal.signal(signal.SIGINT, Pdb._previous_sigint_handler)
+            Pdb._previous_sigint_handler = None
         if self.setup(frame, traceback):
             # no interaction desired at this time (happens if .pdbrc contains
             # a command like "continue")
@@ -1037,7 +1041,7 @@ class Pdb(bdb.Bdb, cmd.Cmd):
         """
         if not self.nosigint:
             try:
-                self._previous_sigint_handler = \
+                Pdb._previous_sigint_handler = \
                     signal.signal(signal.SIGINT, self.sigint_handler)
             except ValueError:
                 # ValueError happens when do_continue() is invoked from

Lib/test/test_pdb.py

@@ -911,6 +911,29 @@ def test_pdb_next_command_subiterator():
     (Pdb) continue
     """
 
+def test_pdb_issue_20766():
+    """Test for reference leaks when the SIGINT handler is set.
+
+    >>> def test_function():
+    ...     i = 1
+    ...     while i <= 2:
+    ...         sess = pdb.Pdb()
+    ...         sess.set_trace(sys._getframe())
+    ...         print('pdb %d: %s' % (i, sess._previous_sigint_handler))
+    ...         i += 1
+
+    >>> with PdbTestInput(['continue',
+    ...                    'continue']):
+    ...     test_function()
+    > <doctest test.test_pdb.test_pdb_issue_20766[0]>(6)test_function()
+    -> print('pdb %d: %s' % (i, sess._previous_sigint_handler))
+    (Pdb) continue
+    pdb 1: <built-in function default_int_handler>
+    > <doctest test.test_pdb.test_pdb_issue_20766[0]>(5)test_function()
+    -> sess.set_trace(sys._getframe())
+    (Pdb) continue
+    pdb 2: <built-in function default_int_handler>
+    """
 
 class PdbTestCase(unittest.TestCase):
 

Misc/NEWS

@@ -107,6 +107,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #20766: Fix references leaked by pdb in the handling of SIGINT
+  handlers.
+
 - Issue #26293: Fixed writing ZIP files that starts not from the start of the
   file.  Offsets in ZIP file now are relative to the start of the archive in
   conforming to the specification.