Considering that this behavior is explicitly called out in the NEWS entries for 3.6.4 and 3.7.0a3, it sounds deliberate to me.

If we really do wantNone as a special case, we should emit a warning (or possibly raise an exception) for other types. cc@serhiy-storchaka, who wrote the code.

Please remember the issue wnd the changelog corresponding to that NEWS entry. I do no remember such issue.

I most likely did not invent that behavior, but simply fixed crashes or error handling in corner cases, or/and synchronized the C and the Python implementations. L9k also at the Python code.

For reference, here is the original issue:#76130 and the PR:#4289. The PR introduced an explicit test forNone:

Thanks,@srittau. What does the corresponding Python code do? There should be a code usingtracebacklimit in thetraceback module.

The only instance is this:

So,Noneis supported, but that might be incidental. The following code basically skips over any frame limiting iflimit isNone, although I'm not sure what that means exactly, as I'm not particular familiar with the traceback module.

The only instance is this:

cpython/Lib/traceback.py

Line 458 in8ba9f5b

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

So,Noneis supported, but that might be incidental. The following code basically skips over any frame limiting iflimit isNone, although I'm not sure what that means exactly, as I'm not particular familiar with the traceback module.

Can supportNone, and this is necessary, this's not a incidental. After thegetattr(sys, 'tracebacklimit', None) statement is executed, it always returns None, because the tracebacklimit attribute does not exist and it never appears insys module.

Running Release|x64 interpreter...Python 3.14.0a0 (heads/master-dirty:ff4e499, Nov 16 2024, 20:59:33) [MSC v.1941 64 bit (AMD64)] on win32Type "help", "copyright", "credits" or "license" for more information.>>> import sys>>> sys.tracebacklimitTraceback (most recent call last):  File "<python-input-1>", line 1, in <module>    sys.tracebacklimitAttributeError: module 'sys' has no attribute 'tracebacklimit'

(It's fix appears in another PR of mine.)

Thanks,@srittau. What does the corresponding Python code do? There should be a code usingtracebacklimit in thetraceback module.

@serhiy-storchaka we no longer have C and Python implementations of the traceback formatting logic. It's all in Python now.

Are there tests for setting it toNone?

There is still C code in_PyTraceBack_Print().

There are tests for settingsys.tracebacklimit to None in test_sys. But the Python implementation in thetraceback module is not tested for this.

And it seems to me that settingsys.tracebacklimit to None has different effect on C and Python implementations.

I think it's vice-versa: we're testing the Python implementation, not the C-level_PyTraceBack_Print. Again though, they seem to do the same thing forNone, at least if my test was extensive enough.