Do not have an extra module for the restriction

python/dune/perftool/__init__.py

+class Restriction:
+    NONE = 0
+    POSITIVE = 1
+    NEGATIVE = 2
\ No newline at end of file

python/dune/perftool/restriction.py

-class Restriction:
-    NONE = 0
-    POSITIVE = 1
-    NEGATIVE = 2
\ No newline at end of file

python/dune/perftool/transformer.py

@@ -7,7 +7,7 @@ import loopy
 import numpy
 import ufl
 
-from dune.perftool.restriction import Restriction
+from dune.perftool import Restriction
 
 # Define the generators that are used here
 from dune.perftool.generation import generator_factory

python/dune/perftool/ufl/modified_terminals.py

 """ A module mimicking some functionality of uflacs' modified terminals """
 
 from ufl.algorithms import MultiFunction
-from dune.perftool.restriction import Restriction
+from dune.perftool import Restriction
 
 
 class ModifiedTerminalTracker(MultiFunction):