'Invokes func() for the single loaded extension.
The signature for func() should be::
def func(ext, *args, **kwds):
pass
The first argument to func(), \'ext\', is the
:class:`~stevedore.extension.Extension` instance.
Exceptions raised from within func() are logged and ignored.
:param func: Callable to invoke for each extension.
:param args: Variable arguments to pass to func()
:param kwds: Keyword arguments to pass to func()
:returns: List of values returned from func()'

def __call__(self, func, *args, **kwds):

    results = self.map(func, *args, **kwds)
    if results:
        return results[0]
