move ResultConverter to core app

core/converters.py

@@ -1,19 +1,16 @@
-class FourDigitYearConverter:
-    regex = "[0-9]{4}"
+from django.urls.converters import IntConverter, StringConverter
 
-    def to_python(self, value):
-        return int(value)
+
+class FourDigitYearConverter(IntConverter):
+    regex = "[0-9]{4}"
 
     def to_url(self, value):
         return str(value).zfill(4)
 
 
-class TwoDigitMonthConverter:
+class TwoDigitMonthConverter(IntConverter):
     regex = "[0-9]{2}"
 
-    def to_python(self, value):
-        return int(value)
-
     def to_url(self, value):
         return str(value).zfill(2)
 
@@ -28,3 +25,9 @@ class BooleanStringConverter:
 
     def to_url(self, value):
         return str(value)
+
+
+class ResultConverter(StringConverter):
+    """Converter whose regex match either "success" or "failure"."""
+
+    regex = "(success|failure)"