Add simplified syntax of kwarg injections for `Callable` provider

dependency_injector/providers.py

@@ -255,22 +255,21 @@ class Callable(Provider):
     with some predefined dependency injections.
     """
 
-    __slots__ = ('_callback', '_injections')
+    __slots__ = ('_callback', '_kwargs')
 
-    def __init__(self, callback, *injections):
+    def __init__(self, callback, **kwargs):
         """Initializer."""
         if not callable(callback):
             raise Error('Callable expected, got {0}'.format(str(callback)))
         self._callback = callback
-        self._injections = tuple((injection
+        self._kwargs = tuple((KwArg(name, value)
-                                  for injection in injections
+                              for name, value in six.iteritems(kwargs)))
-                                  if is_kwarg_injection(injection)))
         super(Callable, self).__init__()
 
     def _provide(self, *args, **kwargs):
         """Return provided instance."""
         return self._callback(*args, **get_injectable_kwargs(kwargs,
-                                                             self._injections))
+                                                             self._kwargs))
 
 
 class Config(Provider):

tests/test_providers.py

@@ -429,9 +429,9 @@ class CallableTests(unittest.TestCase):
     def setUp(self):
         """Set test cases environment up."""
         self.provider = di.Callable(self.example,
-                                    di.KwArg('arg1', 'a1'),
+                                    arg1='a1',
-                                    di.KwArg('arg2', 'a2'),
+                                    arg2='a2',
-                                    di.KwArg('arg3', 'a3'))
+                                    arg3='a3')
 
     def test_init_with_not_callable(self):
         """Test creation of provider with not callable."""
@@ -448,7 +448,7 @@ class CallableTests(unittest.TestCase):
     def test_call_with_args(self):
         """Test provider call with kwargs priority."""
         provider = di.Callable(self.example,
-                               di.KwArg('arg3', 'a3'))
+                               arg3='a3')
         self.assertEqual(provider(1, 2), (1, 2, 'a3'))
 
     def test_call_with_kwargs_priority(self):