Bugs item #1689458, was opened at 2007-03-27 17:07 Message generated for change (Comment added) made by rockyb You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1689458&group_id=5470
Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: Extension Modules Group: None Status: Open Resolution: None Priority: 5 Private: No Submitted By: gotgenes (gotgenes) Assigned to: Nobody/Anonymous (nobody) Summary: pdb unable to jump to first statement Initial Comment: The Python debugger is unable to "jump" back to the first executable statement in a frame once that statement has been executed. For example: [EMAIL PROTECTED]:~/development/playground$ python -m pdb simple.py > /home/chris/development/playground/simple.py(3)?() -> a = 1 (Pdb) next > /home/chris/development/playground/simple.py(4)?() -> b = 2 (Pdb) jump 3 > /home/chris/development/playground/simple.py(3)?() -> a = 1 (Pdb) list 1 #!/usr/bin/env python 2 3 a = 1 4 -> b = 2 5 6 c = a + b 7 8 print c [EOF] (Pdb) next > /home/chris/development/playground/simple.py(6)?() -> c = a + b One can see that after supposedly "jump"ing to line 3 at the second command, when "list"ing the line, the debugger is actually at line 4. The "next" command further demonstrates this since it re-executes line 4 and moves to line 6. This issue was raised on comp.lang.python. (For example, see <http://groups.google.com/group/comp.lang.python/browse_thread/thread/7960201616873f41/e9623c08e3618051> or if that link is munged, refer to <http://tinyurl.com/324feu> Duncan Booth offers the following: [quote] I verified (with a print statement in pdb) that assigning to self.curframe.f_lineno sets self.curframe.f_lineno and sel.curframe.f_lasti incorrectly ... The problem looks to be in frameobject.c: addr = 0; line = f->f_code->co_firstlineno; new_lasti = -1; for (offset = 0; offset < lnotab_len; offset += 2) { addr += lnotab[offset]; line += lnotab[offset+1]; if (line >= new_lineno) { new_lasti = addr; new_lineno = line; break; } } The first bytes in lnotab are the length and line increment for line 3 (i.e. 6, 1). If line==f->f_code->co_firstlineno it should set new_lasti=0, new_lineno=line but the loop still executes once which increments new_lasti and new_lineno to the next line (6, 4). [/quote] And Rocky Bernstein offers the following: [quote] Best as I can tell, it looks like a bug in Python. pdb, pydb, rpdb2 all handle the "jump" command by changing the frame f_lineno value. When the corresponding code pointer has offset 0 (or equivalently and more simlply as you put it, is the first statement) this doesn't seem to work properly. [/quote] ---------------------------------------------------------------------- Comment By: Rocky Bernstein (rockyb) Date: 2007-03-31 06:32 Message: Logged In: YES user_id=158581 Originator: NO Although a single file unit test would be nice, below is a short simple program that I think clearly shows the bug. Alas, as a follow-up comment I don't see a way to attach files so I have to paste it inline. However with this example and the information from Duncan Booth, I think the problem and how to fix it is pretty clear. file: jumpbug.py #!/usr/bin/env python import inspect, linecache, sys def tracer(frame, event, arg): global z (filename, line_no) = inspect.getframeinfo(frame)[0:2] print "Event %s at line %d:" % (event, line_no) print "\t", linecache.getline(filename, line_no), print "----------------------" try: if z == 0: if line_no == 4: print "***We jumped back to line 4 but should have gone to 2**" sys.exit(1) frame.f_lineno = 2 # And 3 is broken too. except NameError: pass return tracer # This helps emacs figure indentation out sys.settrace(tracer) execfile("jumpbug2.py") #END first file file jumpbug2.py: #!/usr/bin/env python x = 2 # This statement gets skipped the 2nd time around q = 1 # This statement gets skipped too! try: # tracer() will exit here if z == 0 and line_no == 4 y = z except NameError: z = 0 print "When tracing via tracer(), f_lineno will be set to 2 here." print "You should never get here when tracing" file jumpbug2.py: ---------------------------------------------------------------------- Comment By: gotgenes (gotgenes) Date: 2007-03-28 21:24 Message: Logged In: YES user_id=1180453 Originator: YES Truthfully, I don't have enough know-how to write a full test case or a patch. I have put forth a request on the comp.lang.python thread (link in original report) for those that would to please do so. ---------------------------------------------------------------------- Comment By: Collin Winter (collinwinter) Date: 2007-03-28 17:54 Message: Logged In: YES user_id=1344176 Originator: NO Could you work up a full test case for this? Or better yet, a patch? ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1689458&group_id=5470 _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
