[PATCH evemu] python: call only once the libevdev backend per request

[Daniel Martin]

On 2 September 2014 09:29, Daniel Martin <consume.noise at gmail.com> wrote:
> On Tue, Sep 02, 2014 at 04:42:05PM +1000, Peter Hutterer wrote:
>> On Fri, Aug 29, 2014 at 05:34:16PM -0400, Benjamin Tissoires wrote:
>> > We can factorize some code, and provide a cleaner way of implementing
>> > event_get_value(), event_get_name(), input_prop_get_name() and
>> > input_prop_get_value()
>> >
>> > Signed-off-by: Benjamin Tissoires <benjamin.tissoires at gmail.com>
>> > ---
>> >  python/evemu/__init__.py | 112 ++++++++++++++++++++++++++---------------------
>> >  1 file changed, 62 insertions(+), 50 deletions(-)
>> >
>> > diff --git a/python/evemu/__init__.py b/python/evemu/__init__.py
>> > index 65e4673..22035b8 100644
>> > --- a/python/evemu/__init__.py
>> > +++ b/python/evemu/__init__.py
>> > @@ -37,6 +37,54 @@ __all__ = ["Device",
>> >
>> >  _libevdev = evemu.base.LibEvdev()
>> >
>> > +def _event_type_get_value_name(event_type):
>> > +    event_type_value = event_type_name = None
>> > +
>> > +    if isinstance(event_type, int):
>> > +        event_type_name = _libevdev.libevdev_event_type_get_name(event_type)
>> > +        if event_type_name == None:
>>
>> shouldn't that be 0 for NULL?
>
> Neither. Just was curious myself and tested it.
>
> - Everything returning a pointer should be sufficient for testing what
>   happens if it returns NULL. Use malloc() and say that it returns a
>   c_char_p:
>
>     >>> from ctypes import *
>     >>> libc = CDLL("libc.so.6")
>     >>> libc.malloc.restype = c_char_p
>     >>> libc.malloc.argtypes = [c_size_t]
>
>     >>> ptr = libc.malloc(0)
>
> - Aaaah ...
>
>     >>> type(ptr)
>     <class 'bytes'>
>
> - As it is an (bytes) object, the test with None doesn't work:
>
>     >>> ptr is None
>     False
>
> - But, a test on its length is possible:
>
>     >>> len(ptr)
>     0

If we want to make it behave a bit more C-like (get None in case of NULL),
we could set an errcheck function for libevdev_event_type_get_name()
(Just tested in interactive mode with the short example from above and
used a lambda to make it short):

    _api_prototypes = {
        #const char *libevdev_event_type_get_name(unsigned int type);
        "libevdev_event_type_get_name": {
            "argtypes": (c_uint,),
            "restype": c_char_p,
            "errcheck": lambda res, func, args: res if len(res) else None,
            },
        ...