On 09/12/2010 20:23, Eric Frederich wrote:
I am attempting to automate the building of binding for a 3rd party library.
The functions I'm wrapping all return an integer of whether they
failed and output are passed as pointers.
There can be multiple return values.
So the code that I generate has a PyObject* called python__return_val
that I use for returning.
In the 'wrapped_foo' function below you see I build the return value
with Py_BuildValue and "OO" as the format.
For every output I have I do a C to Python conversion and add another
'O' to the format.
What I'm wondering is if I can use the same logic when wrapping
functions that only return one value like the wrapped_bar function
below.
So for multiples, I wind up doing this which is fine.
python__x = Py_BuildValue("s", x)
The object at python__x has a refcount of 1.
python__y = Py_BuildValue("s", y)
The object at python__y has a refcount of 1.
python__return_val = Py_BuildValue("OO", python__x, python__y);
The object at python__return_val (a tuple) has a refcount of 1. This
object refers to the objects at python__x and python__y, so both of
their refcounts will have been incremented to 2. You will need to
DECREF the objects at python__x and python__y before the C variables
python__x and python__y go out of scope.
But for single returns I do something like this....
I realize that the 2 lines below are pointless, but are they causing a
memory leak or problems with reference counting?
python__x = Py_BuildValue("s", x)
The object at python__x has a refcount of 1.
python__return_val = Py_BuildValue("O", python__x);
In this case Py_BuildValue returns its argument python__x, but will
have incremented its refcount to 2. This means that you still need to
DECREF the object at python__x before the C variable python__x goes out
of scope.
This is probably just for consistency, because it's easier to remember
that /every time/ you pass an object to Py_BuildValue its refcount will
be incremented, than if it was sometimes yes, sometimes no.
Are python__x and python__return_val the same object, a copy of the object?
Would python__x ever get garbage collected?
Should my code generator detect when there is only one output and not
go through the extra step?
[snip]
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