While PyErr_SetString is obvious that you do not have to worry about the reference count of 'exception', the documentation for PyErr_SetObject is silent on whether it steals or adds a reference to 'value'.  This is particularly confusing, since other functions on the page (like PyErr_Restore) are explicit about stealing references.  Looking at non-canonical documentation, I found https://docstore.mik.ua/orelly/other/python/0596001886_pythonian-chp-24-sect-1.html which claims PyErr_SetObject steals a reference to 'value'.  But that is wrong; looking at the source code for _PyErr_SetString, it becomes obvious that once you use SetObject, the reference count will be increased, and the caller can release its own reference because nothing was stolen.

I noticed this lack of documentation when trying to debug a memory leak in nbdsh: https://listman.redhat.com/archives/libguestfs/2021-November/msg00280.html

The default behaviour of functions is to not steal references, in general only exceptions to this are documented. Likewise with return values: by default the result is a strong reference, and borrowed references are documented as such.

I concur with Ronald. If we explicitly document that PyErr_SetObject() does not steal reference we would need to document it for every parameter of every function. It would make the documentation worse because it would be more difficult to distinguish ouliners which steal references from normal functions which does not steal references.

Use official Python documentation.