All the problems raised in this issue are caused by self.botframe being set in a Pdb frame. In the following pdb session run with python 3.2.2, the first two frames in the printed stack are Pdb frames, this is wrong. And the second step command steps incorrectly into the exec() frame that is called by the Bdb run() method. What prevents the third step command to step into the run() frame, is that this frame does not have a trace function setup initially. === foo.py ================================= i = 1 ================================================= $ python3 -m pdb foo.py > path_to/foo.py(1)<module>() -> i = 1 (Pdb) import sys; print(sys.version) 3.2.2 (default, Dec 27 2011, 17:35:55) [GCC 4.3.2] (Pdb) where /usr/local/lib/python3.2/bdb.py(392)run() -> exec(cmd, globals, locals) <string>(1)<module>() > path_to/foo.py(1)<module>() -> i = 1 (Pdb) step --Return-- > path_to/foo.py(1)<module>()->None -> i = 1 (Pdb) step --Return-- > <string>(1)<module>()->None (Pdb) step The program finished and will be restarted > path_to/foo.py(1)<module>() -> i = 1 (Pdb) quit ================================================= In the following pdb session run with python built from the default branch (i.e. after issue 13183 has been fixed) the third step command steps into the run() method of Bdb and the backtrace printed after the quit command shows duplicate entries. Pdb is trying to debug itself ! Pdb steps in the run() method because after the fix in issue 13183, Pdb knows now how to step when returning into the caller frame with no trace function. === foo.py ================================= i = 1 ================================================= $ python -m pdb foo.py > path_to/foo.py(1)<module>() -> i = 1 (Pdb) step --Return-- > path_to/foo.py(1)<module>()->None -> i = 1 (Pdb) step --Return-- > <string>(1)<module>()->None (Pdb) step > path_to/cpython/Lib/bdb.py(409)run() -> self.quitting = True (Pdb) quit Traceback (most recent call last): File "path_to/cpython/Lib/pdb.py", line 1651, in main pdb._runscript(mainpyfile) File "path_to/cpython/Lib/pdb.py", line 1532, in _runscript self.run(statement) File "path_to/cpython/Lib/bdb.py", line 409, in run self.quitting = True File "path_to/cpython/Lib/bdb.py", line 409, in run self.quitting = True File "path_to/cpython/Lib/bdb.py", line 47, in trace_dispatch return self.dispatch_line(frame) File "path_to/cpython/Lib/bdb.py", line 66, in dispatch_line if self.quitting: raise BdbQuit bdb.BdbQuit Uncaught exception. Entering post mortem debugging Running 'cont' or 'step' will restart the program > path_to/cpython/Lib/bdb.py(66)dispatch_line() -> if self.quitting: raise BdbQuit (Pdb) quit Post mortem debugger finished. The foo.py will be restarted > path_to/foo.py(1)<module>() -> i = 1 (Pdb) quit ================================================= In the following pdb session run with python 3.2.2, the session is interrupted with <Ctl-C>. The same problems occur as in the previous case. ================================================= import time i = 1 while i: time.sleep(.100) i = 0 ================================================= $ python3 -m pdb foo.py > path_to/foo.py(1)<module>() -> import time (Pdb) import sys; print(sys.version) 3.2.2 (default, Dec 27 2011, 17:35:55) [GCC 4.3.2] (Pdb) continue ^C Program interrupted. (Use 'cont' to resume). > path_to/foo.py(3)<module>() -> while i: (Pdb) !i=0 (Pdb) step > path_to/foo.py(5)<module>() -> i = 0 (Pdb) step --Return-- > path_to/foo.py(5)<module>()->None -> i = 0 (Pdb) step --Return-- > <string>(1)<module>()->None (Pdb) step > /usr/local/lib/python3.2/bdb.py(396)run() -> self.quitting = True (Pdb) quit Traceback (most recent call last): File "/usr/local/lib/python3.2/pdb.py", line 1556, in main pdb._runscript(mainpyfile) File "/usr/local/lib/python3.2/pdb.py", line 1437, in _runscript self.run(statement) File "/usr/local/lib/python3.2/bdb.py", line 396, in run self.quitting = True File "/usr/local/lib/python3.2/bdb.py", line 396, in run self.quitting = True File "/usr/local/lib/python3.2/bdb.py", line 46, in trace_dispatch return self.dispatch_line(frame) File "/usr/local/lib/python3.2/bdb.py", line 65, in dispatch_line if self.quitting: raise BdbQuit bdb.BdbQuit Uncaught exception. Entering post mortem debugging Running 'cont' or 'step' will restart the program > /usr/local/lib/python3.2/bdb.py(65)dispatch_line() -> if self.quitting: raise BdbQuit (Pdb) quit Post mortem debugger finished. The foo.py will be restarted > path_to/foo.py(1)<module>() -> import time (Pdb) quit ================================================= The attached patch fixes all those problems. The patch applies to the default branch.