On 2020-01-07 20:37, Rui Hu wrote:
I see! That definitely helps. What about a call to
PyObject_CallMethodObjArgs()? Under the hood, is it really the same as a first
call to PyObject_GetAttr() to get an attribute which is followed by another
call to PyObject_Call()? I read Objects/call.c and seems to me this is the
case. I'm asking because with Py_VaBuildValue() the only to simulate
Py_CallMethodObjArgs() is the two-way call described above.
It returns a new reference because it's returning a result, which might
be a newly-created object.
Consider, say, PyList_GetItem. The object it returns is in the list, so
doing an incref would be wasteful (you're not expecting the object to
disappear unexpectedly). It's a borrowed reference, and that's good enough.
Now consider PyUnicode_Substring. The result is a substring, so some
copying must take place. A new string is created and returned. It
returns a new reference.
Except that it doesn't always create a new string.
If the substring happens to include all of the characters, there's no
need to make a copy, because strings are immutable. It'll just do an
incref and return the original string, and your code will be none the wiser.
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