Python implementation of traceback limit does not default to 1000 as documented in 3.13

[blhsing]

Bug report

Bug description:

According to the documentation of sys.tracebacklimit, it should default to 1000 if not set, so the following snippet:

import sys

def f():
    f()

sys.setrecursionlimit(2000)
f()

produces a traceback of 1000 frames as expected in 3.12:

Traceback (most recent call last):
  File "t.py", line 4, in f
    f()
    ~^^
  File "t.py", line 4, in f
    f()
    ~^^
  File "t.py", line 4, in f
    f()
    ~^^
  [Previous line repeated 997 more times]
RecursionError: maximum recursion depth exceeded

But in 3.13 and the current master, it produces a traceback of all 2000 frames:

Traceback (most recent call last):
  File "t.py", line 4, in f
    f()
    ~^^
  File "t.py", line 4, in f
    f()
    ~^^
  File "t.py", line 4, in f
    f()
    ~^^
  File "t.py", line 4, in f
    f()
    ~^^
  [Previous line repeated 1996 more times]
RecursionError: maximum recursion depth exceeded

This is because with issue #110721, traceback is now printed with the traceback module by default, and the traceback module defaults sys.tracebacklimit to None when not set:

cpython/Lib/traceback.py

Line 458 in c3ed775

limit = getattr(sys, 'tracebacklimit', None)

whereas the C implementation of the traceback printer has a proper default of 1000 for sys.tracebacklimit as documented:

cpython/Python/traceback.c

Line 707 in c3ed775

#define PyTraceBack_LIMIT 1000

I will submit a PR to make 1000 the default value for sys.tracebacklimit in the Python implementation of the traceback module.

CPython versions tested on:

3.13, CPython main branch

Operating systems tested on:

Linux, Windows

Linked PRs

• gh-123596: Add missing tracebacklimit attribute to sys module #125719
• gh-123596: Fixed return None when getattr the sys.tracebacklimit. #125777

[cfbolz]

Nice find! When fixing you need to be careful not to change the behavior for existing explicit users of the traceback module. The traceback module has a special sentinel that is passed for 'builtin' traceback formatting, look for builtin_limit.

[rruuaanng]

Are you still studying the problem? If you are ready to submit, maybe I will close my submission. Be sorry.:)

[blhsing]

Are you still studying the problem? If you are ready to submit, maybe I will close my submission. Be sorry.:)

I went with the limit = getattr(sys, 'tracebacklimit', 1000) route in my attempt to fix the bug but had been dealing with a failed existing test. I think your approach of simply setting sys.tracebacklimit to 1000 is both easier and cleaner. 👍

[rruuaanng]

I have fixed the C code regarding the sys.tracebacklimit attribute. I can close that commit in python so that your changes to traceback.py can be initiated. What do you think?

[rruuaanng]

I have closed the PR for traceback.py. I'm sorry, but this is not a simple traceback.py problem. There is no sys.tracebacklimit attribute in sys. I have submitted the PR. You can continue to fix traceback.py.

[rruuaanng]

@blhsing Are you still working on it? If you are done, you can submit a PR. My PR is waiting for your submission before it can be merged.