classification
Title: Tracing disabled when a recursion error is triggered (even if properly handled)
Type: behavior Stage:
Components: Interpreter Core Versions: Python 3.4, Python 3.5, Python 2.7
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: fabioz, gphemsley, james, pdmccormick, r.david.murray
Priority: normal Keywords: patch

Created on 2011-01-18 12:31 by fabioz, last changed 2019-05-18 01:26 by gphemsley.

Files
File name Uploaded Description Edit
recursion_error_disables_tracing.py fabioz, 2011-01-18 12:31 Recursion error (test case)
issue_10933.patch james, 2015-04-13 01:08 documentation patch for sys.settrace [Doc/library/sys.rst] review
issue_10933-2.patch pdmccormick, 2015-04-13 01:11 Revised patch review
Messages (6)
msg126460 - (view) Author: Fabio Zadrozny (fabioz) Date: 2011-01-18 12:31
It seems that tracing in the interpreter is lost after some recursion error is triggered (even if it's properly handled).

This breaks any debugger working after any recursion error is triggered (which suppose shouldn't happen).

The attached test case shows the problem in action.

Tested the problem with Python 2.6.5 and 3.1.3
msg220891 - (view) Author: Mark Lawrence (BreamoreBoy) * Date: 2014-06-17 21:04
Can we have a response to this please.
msg240578 - (view) Author: James Powell (james) Date: 2015-04-13 01:08
We investigated this issue with pdmccormick & r.david.murray.

The behaviour appears to be intentional. If the trace function raises an Exception, system tracing is disabled entirely.

See attached documentation patch to clarify this.
msg240579 - (view) Author: Peter McCormick (pdmccormick) * Date: 2015-04-13 01:11
Removed unrelated doc changes.
msg240584 - (view) Author: R. David Murray (r.david.murray) * (Python committer) Date: 2015-04-13 02:10
We also discussed whether or not it would be worth indicating in the exception that tracing has been disabled.  I believe that implementing this would be aided by resolution of issue 23188.  Doing a chained exception for this would also make it clearer that the exception happened inside the trace function.

It is not clear that it is sensible to allow tracing to continue if the trace function raises an error, since that pretty much leaves the tracer or debugger or what have you in an undefined state.  It is also not clear that there is any reasonable way to try to avoid a recursion error in the trace function when we are near the recursion limit in the underlying code, since the stack depth of the trace function is pretty much arbitrary.
msg240599 - (view) Author: Fabio Zadrozny (fabioz) Date: 2015-04-13 10:58
Well, I'd say that if tracing is enabled and is disabled automatically by Python (thus breaking a working debugger which would usually be used to diagnose the error), I'd at least consider issuing some warning to stderr... (probably warnings.warn cannot be used directly as the stack is at its max depth, but a choice could be raising the max depth, using warnings.warn and then restoring the max depth value in a try..finally -- or at least printing something to stderr regardless of warnings.warn).

I.e.: as this is a rare situation and should only happen when you're debugging, I think printing something to stderr regarding that is definitely worth it regardless of chained exceptions (on many cases I had to help users instrument a simple tracer just to detect where it was disabled -- yes, on some of those they were catching all exceptions on some block -- so, program which worked with the recursion stopped having a working debugger).
History
Date User Action Args
2019-05-18 01:26:48gphemsleysetnosy: + gphemsley
2019-03-15 22:10:52BreamoreBoysetnosy: - BreamoreBoy
2018-06-12 22:30:19belopolskylinkissue33849 superseder
2015-04-13 10:58:38fabiozsetmessages: + msg240599
2015-04-13 02:10:11r.david.murraysetmessages: + msg240584
2015-04-13 01:11:41pdmccormicksetfiles: + issue_10933-2.patch

messages: + msg240579
2015-04-13 01:08:19jamessetfiles: + issue_10933.patch
keywords: + patch
messages: + msg240578
2015-04-13 01:04:48jamessetnosy: + r.david.murray, james
2015-04-13 01:03:38pdmccormicksetnosy: + pdmccormick
2014-06-17 21:04:36BreamoreBoysetnosy: + BreamoreBoy

messages: + msg220891
versions: + Python 2.7, Python 3.4, Python 3.5, - Python 2.6, Python 3.1
2011-01-18 12:31:08fabiozcreate