Fix is_simple_callable with variable args, kwargs

Author: Ryan P Kilby

rest_framework/fields.py

@@ -59,7 +59,12 @@ def is_simple_callable(obj):
 
         sig = inspect.signature(obj)
         params = sig.parameters.values()
-        return all(param.default != param.empty for param in params)
+        return all(
+            param.kind == param.VAR_POSITIONAL or
+            param.kind == param.VAR_KEYWORD or
+            param.default != param.empty
+            for param in params
+        )
 
 else:
     def is_simple_callable(obj):

tests/test_fields.py

@@ -37,6 +37,9 @@ def valid(self):
             def valid_kwargs(self, param='value'):
                 pass
 
+            def valid_vargs_kwargs(self, *args, **kwargs):
+                pass
+
             def invalid(self, param):
                 pass
 
@@ -45,11 +48,13 @@ def invalid(self, param):
         # unbound methods
         assert not is_simple_callable(Foo.valid)
         assert not is_simple_callable(Foo.valid_kwargs)
+        assert not is_simple_callable(Foo.valid_vargs_kwargs)
         assert not is_simple_callable(Foo.invalid)
 
         # bound methods
         assert is_simple_callable(Foo().valid)
         assert is_simple_callable(Foo().valid_kwargs)
+        assert is_simple_callable(Foo().valid_vargs_kwargs)
         assert not is_simple_callable(Foo().invalid)
 
     def test_function(self):
@@ -59,11 +64,15 @@ def simple():
         def valid(param='value', param2='value'):
             pass
 
+        def valid_vargs_kwargs(*args, **kwargs):
+            pass
+
         def invalid(param, param2='value'):
             pass
 
         assert is_simple_callable(simple)
         assert is_simple_callable(valid)
+        assert is_simple_callable(valid_vargs_kwargs)
         assert not is_simple_callable(invalid)
 
     @unittest.skipUnless(typings, 'requires python 3.5')