Re: [Libguestfs] [PATCH nbdkit v2 03/10] python: Implement nbdkit API version 2.
On Fri, Nov 22, 2019 at 11:35 PM Eric Blake <eblake(a)redhat.com> wrote:
On 11/22/19 3:20 PM, Nir Soffer wrote:
>>> +# There are several variants of the API. nbdkit will call this
>>> +# function first to determine which one you want to use. This is the
>>> +# latest version at the time this example was written.
>>> +def api_version():
>>> + return 2
>>
>> Matches the C counterpart of #define NBDKIT_API_VERSION 2 at the top of
>> a plugin.
>
> This is the same thing I was thinking about. This makes it more clear
> that the api
> version is constant, and not something the plugin should change while
> it is being used.
Hmm - api_version() really is constant for the entire life of nbdkit. We
call it exactly once. Figuring out how to read a Python variable
instead of calling a function would be slightly more in line with the
fact that in C code it is a #define constant rather than a function
pointer callback. But it is that much more glue code to figure out how
to check for a python global variable, compared to the glue code we
already have for calling a python function.
The extra glue code is (without error handling):
PyObject *d = PyModule_GetDict(PyObject *module);
PyObject *v = PyDict_GetItemString(d, "API_VERSION");
long api_version = PyLong_AsLong(v);