GeezerVison

Would you mind to give examples? I'm not sure how to use this API.

I understood that PyErr_WriteUnraisable(obj) can be written as:

PyErr_FormatUnraisable("Exception ignored in: %R", obj);

And without an exception an object, it should be:

PyErr_FormatUnraisable("Exception ignored in:");

Do the format must end with a newline character?

If format is NULL, only the traceback is printed.

What's the usage of this mode? Is the caller expected to log something like "Exception ignored in xxx" manually?

PyErr_FormatUnraisable(NULL) is the same as PyErr_WriteUnraisable(NULL). It just prints the traceback, without "Exception ignored ...".

I simply documented the existing behavior for PyErr_WriteUnraisable(), and for PyErr_FormatUnraisable(NULL) the most natural way is to do the same. What alternative do you propose?

Sorry, my remark is not specific to NULL value, but more about the whole function. I don't know which string to pass to the function. I suggest to add an example to the doc. Like:

For example, ``PyErr_WriteUnraisable(obj)`` is similar to ``PyErr_FormatUnraisable("Exception ignored in: %R", obj);``.

PyErr_FormatUnraisable(NULL) is the same as PyErr_WriteUnraisable(NULL). It just prints the traceback, without "Exception ignored ...".

I simply documented the existing behavior for PyErr_WriteUnraisable(), and for PyErr_FormatUnraisable(NULL) the most natural way is to do the same. What alternative do you propose?

TODO: This test should be backported.

See #111455.

Sorry, my remark is not specific to NULL value, but more about the whole function. I don't know which string to pass to the function. I suggest to add an example to the doc. Like:

For example, ``PyErr_WriteUnraisable(obj)`` is similar to ``PyErr_FormatUnraisable("Exception ignored in: %R", obj);``.

I would prefer to log an error in the error handler in this case. Ignoring silently errors doesn't help :-(

_PyErr_WriteUnraisableMsg() does the same: silently ignores decoding and memory errors.

I minimized changes. Other changes can be made in a separate PR.

Would it be possible to move obj to end, last parameter?

Sure. But I would make the order of arguments inconsistent in format_unraisable() and format_unraisable_v().

I don't think that it's the best behavior. I would prefer to goto error. What do you think?

Maybe PyUnicode_FromString("Exception ignored in sys.unraisablehook") can become a _Py_DECLARE_STR(exc_ignored_msg, "...") + _Py_STR(exc_ignored_msg) static immortal string to avoid error 3 while handling error 2 while handling error 1.

It is the same as in _PyErr_WriteUnraisableMsg(). Changing the behavior of _PyErr_WriteUnraisableMsg() is out of the scope of this PR.