Add another sample for user defined enum.

py_samples/import_enum_and_print_udt.py

@@ -0,0 +1,19 @@
+import enum
+
+class MyEnum(enum.Enum):
+    MY = 'my'
+    ENUMERATED = 'enumerated'
+    ITEMS = 'items'
+
+
+e = MyEnum.MY
+assert e == MyEnum.MY
+assert e == MyEnum('my')
+assert e != MyEnum('enumerated')
+assert isinstance(e, MyEnum), e
+
+s = str(e)
+assert s == 'MyEnum.MY', s
+r = repr(e)
+assert r == "<MyEnum.MY: 'my'>", r
+print(e)

src/echo/builtin_predicates.py

@@ -32,6 +32,7 @@ def _do_bool_call(args: Tuple[Any, ...],
                               types.BuiltinFunctionType,
                               types.MethodDescriptorType,
                               getattr(_thread, 'RLock'), io.TextIOBase,
+                              type(NotImplemented),
                               type(None), getattr(re, 'Match'))), \
             (o, type(o))
         return Result(bool(o))