Use shorter 'if kwargs' check as requested during review

_pytest/python_api.py

@@ -597,7 +597,7 @@ def raises(expected_exception, *args, **kwargs):
             message = kwargs.pop("message")
         if "match" in kwargs:
             match_expr = kwargs.pop("match")
-        if len(kwargs.keys()) > 0:
+        if kwargs:
             msg = 'Unexpected keyword arguments passed to pytest.raises: '
             msg += ', '.join(kwargs.keys())
             raise TypeError(msg)