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Title: Generators break trace functionality
Type: behavior Stage:
Components: Interpreter Core Versions: Python 2.6, Python 2.5
Status: closed Resolution: duplicate
Dependencies: Superseder: pdb bug with "with" statement
View: 1265
Assigned To: Nosy List: cortesi, gvanrossum
Priority: normal Keywords:

Created on 2007-11-17 07:28 by cortesi, last changed 2022-04-11 14:56 by admin. This issue is now closed.

File name Uploaded Description Edit
generator-trace.patch cortesi, 2007-11-17 07:28
Messages (4)
msg57598 - (view) Author: Aldo Cortesi (cortesi) Date: 2007-11-17 07:28
I rely heavily on a code coverage analysis engine I developed, and a bug
in Python's trace functionality has been bothering me for years. Today I
snapped, and finally tracked it down to a minimal test case. To see the
problem, play with the following code:

import sys

def run(): yield 1

def trace(frame, event, arg):
        for i in []: pass
    except Exception, e:

x = run()
del x

Remove the try clause, and re-run with a debug build of the interpreter
for a different symptom. Add a print statement at the end to verify that
the problem occurs when the generator object is deleted.

The problem occurs due to an interaction between generators and the
trace functionality. When a generator is deleted, the gen_del function
calls gen_close, which then sets a GeneratorExit exception. Eventually,
PyEval_EvalFrameEx is called, with the throwflag set. At this point the
trace function is called, the GeneratorExit exception which is set
causes problems with the FOR_ITER opcode, which then fails.

The attached patch against trunk fixes this by storing exceptions before
the call trace function is called, and restoring the exception
afterwards. All regression tests pass for me with this patch applied.
msg57604 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2007-11-17 15:49
I think this was fixed in svn this week!  See issue 1265.  Let me know
if your issue is different.
msg57607 - (view) Author: Aldo Cortesi (cortesi) Date: 2007-11-17 21:11
Drat, you're right. This was fixed a few days ago by Amaury in 

Another example of confluence - this bug has existed for a very long time.
msg57608 - (view) Author: Guido van Rossum (gvanrossum) * (Python committer) Date: 2007-11-17 22:27
Thanks anyway!
Date User Action Args
2022-04-11 14:56:28adminsetgithub: 45795
2007-11-17 22:27:59gvanrossumsetstatus: open -> closed
resolution: duplicate
superseder: pdb bug with "with" statement
messages: + msg57608
2007-11-17 21:11:44cortesisetmessages: + msg57607
2007-11-17 15:49:05gvanrossumsetnosy: + gvanrossum
messages: + msg57604
2007-11-17 07:28:58cortesicreate