ENH: Don't allow instantiating interfaces.

Author: Scott Sanderson

interface/interface.py

@@ -144,6 +144,8 @@ class Interface(metaclass=InterfaceMeta):
     """
     Base class for interface definitions.
     """
+    def __new__(cls, *args, **kwargs):
+        raise TypeError("Can't instantiate interface %s" % getname(cls))
 
 
 empty_set = frozenset([])

interface/tests/test_interface.py

@@ -287,3 +287,12 @@ def method3(self, a, b, c):
         OtherIFace.method3(self, a, b, c)"""
     )
     assert impl.__doc__ == expected_doc
+
+
+def test_cant_instantiate_interface():
+
+    class I(Interface):  # pragma: nocover
+        pass
+
+    with pytest.raises(TypeError):
+        I()