diff --git a/Lib/bdb.py b/Lib/bdb.py
index c6a10359ac..6872186683 100644
--- a/Lib/bdb.py
+++ b/Lib/bdb.py
@@ -3,6 +3,8 @@
 import fnmatch
 import sys
 import os
+import linecache
+import reprlib
 from inspect import CO_GENERATOR, CO_COROUTINE, CO_ASYNC_GENERATOR
 
 __all__ = ["BdbQuit", "Bdb", "Breakpoint"]
@@ -53,7 +55,6 @@ class Bdb:
 
     def reset(self):
         """Set values of attributes as ready to start debugging."""
-        import linecache
         linecache.checkcache()
         self.botframe = None
         self._set_stopinfo(None, None)
@@ -89,7 +90,11 @@ class Bdb:
         if event == 'call':
             return self.dispatch_call(frame, arg)
         if event == 'return':
-            return self.dispatch_return(frame, arg)
+            try:
+                return self.dispatch_return(frame, arg)
+            finally:
+                if frame == self.botframe:
+                    self.botframe = None
         if event == 'exception':
             return self.dispatch_exception(frame, arg)
         if event == 'c_call':
@@ -123,8 +128,11 @@ class Bdb:
         # XXX 'arg' is no longer used
         if self.botframe is None:
             # First call of dispatch since reset()
-            self.botframe = frame.f_back # (CT) Note that this may also be None!
-            return self.trace_dispatch
+            self.botframe = frame.f_back
+            # When tracing a destructor, frame.f_back is None and the 'call'
+            # trace event is not ignored.
+            if frame.f_back is not None:
+                return self.trace_dispatch
         if not (self.stop_here(frame) or self.break_anywhere(frame)):
             # No need to trace this function
             return # None
@@ -371,7 +379,6 @@ class Bdb:
         The filename should be in canonical form.
         """
         filename = self.canonic(filename)
-        import linecache # Import as late as possible
         line = linecache.getline(filename, lineno)
         if not line:
             return 'Line %s:%d does not exist' % (filename, lineno)
@@ -538,7 +545,6 @@ class Bdb:
         line of code (if it exists).
 
         """
-        import linecache, reprlib
         frame, lineno = frame_lineno
         filename = self.canonic(frame.f_code.co_filename)
         s = '%s(%r)' % (filename, lineno)
@@ -843,7 +849,6 @@ class Tdb(Bdb):
         if not name: name = '???'
         print('+++ call', name, args)
     def user_line(self, frame):
-        import linecache
         name = frame.f_code.co_name
         if not name: name = '???'
         fn = self.canonic(frame.f_code.co_filename)
diff --git a/Lib/pdb.py b/Lib/pdb.py
index fb23ae3e6a..ed28a90efa 100755
--- a/Lib/pdb.py
+++ b/Lib/pdb.py
@@ -80,6 +80,7 @@ import signal
 import inspect
 import traceback
 import linecache
+import shlex
 
 
 class Restart(Exception):
@@ -609,6 +610,10 @@ class Pdb(bdb.Bdb, cmd.Cmd):
         hasn't been loaded yet).  The file is searched for on
         sys.path; the .py suffix may be omitted.
         """
+        if sys.path is None:
+            self.error('Cannot set a breakpoint, sys.path is None')
+            return
+
         if not arg:
             if self.breaks:  # There's at least one
                 self.message("Num Type         Disp Enb   Where")
@@ -1021,7 +1026,6 @@ class Pdb(bdb.Bdb, cmd.Cmd):
         are preserved.  "restart" is an alias for "run".
         """
         if arg:
-            import shlex
             argv0 = sys.argv[0:1]
             sys.argv = shlex.split(arg)
             sys.argv[:0] = argv0
@@ -1635,7 +1639,11 @@ def test():
 
 # print help
 def help():
-    import pydoc
+    try:
+        import pydoc
+    except ImportError:
+        print('***', 'Cannot print pdb main help on Python finalization')
+        return
     pydoc.pager(__doc__)
 
 _usage = """\
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 343c5a4440..457dd88804 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -2469,6 +2469,7 @@ class StatefulIncrementalDecoderTest(unittest.TestCase):
         self.assertEqual(d.decode(b'', 1), 'abcd.')
 
 class TextIOWrapperTest(unittest.TestCase):
+    shutdown_error = "LookupError: unknown encoding: ascii"
 
     def setUp(self):
         self.testdata = b"AAA\r\nBBB\rCCC\r\nDDD\nEEE\r\n"
@@ -3567,7 +3568,6 @@ def _to_memoryview(buf):
 
 class CTextIOWrapperTest(TextIOWrapperTest):
     io = io
-    shutdown_error = "RuntimeError: could not find io module state"
 
     def test_initialization(self):
         r = self.BytesIO(b"\xc3\xa9\n\n")
@@ -3613,7 +3613,6 @@ class CTextIOWrapperTest(TextIOWrapperTest):
 
 class PyTextIOWrapperTest(TextIOWrapperTest):
     io = pyio
-    shutdown_error = "LookupError: unknown encoding: ascii"
 
 
 class IncrementalNewlineDecoderTest(unittest.TestCase):
diff --git a/Python/import.c b/Python/import.c
index bb1d69e168..80f96347f5 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -503,6 +503,15 @@ PyImport_Cleanup(void)
         }
     }
 
+    /* Modules whose only referrer was sys.modules are now cleared by this
+     * garbage collection. This is the last chance to trace destructors as
+     * tracing in the next garbage collection made after the call to
+     * _PyState_ClearModules() may fail because PyState_FindModule() for
+     * extension modules returns NULL at that time (pdb calls into the
+     * readline extension module). */
+    _PyGC_CollectNoFail();
+    PyEval_SetTrace(NULL, NULL);
+
     /* Clear the modules dict. */
     if (PyDict_CheckExact(modules)) {
         PyDict_Clear(modules);