UniqueObject

create a class to be used for unique objects.
better for debugging and documentation than just using object()

+ remove unused unique objects

Change-Id: I32f65960ea2fbee4fccbeb49a4e11176b7185aa0
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/27455
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/properties.py

@@ -26,8 +26,11 @@
 import inspect
 
 from secop.errors import BadValueError, ConfigError, ProgrammingError
+from secop.lib import UniqueObject
 from secop.lib.py35compat import Object
 
+UNSET = UniqueObject('undefined value')  #: an unset value, not even None
+
 
 class HasDescriptors(Object):
     @classmethod
@@ -39,9 +42,6 @@ class HasDescriptors(Object):
             raise ProgrammingError('misplaced trailing comma after %s.%s' % (cls.__name__, '/'.join(bad)))
 
 
-UNSET = object()  # an unset value, not even None
-
-
 # storage for 'properties of a property'
 class Property:
     """base class holding info about a property