Řetězce není dobré porovnávat pomocí "is"

mo/place_level.py

@@ -13,15 +13,15 @@ class PlaceLevel:
 
     def name_genitive(self, m="", f="", n="") -> str:
         w = {'m': m, 'f': f, 'n': n}[self.genus]
-        return (w + ' ' if w is not '' else '') + self.name_gen
+        return (w + ' ' if w != '' else '') + self.name_gen
 
     def name_accusative(self, m="", f="", n="") -> str:
         w = {'m': m, 'f': f, 'n': n}[self.genus]
-        return (w + ' ' if w is not '' else '') + self.name_acc
+        return (w + ' ' if w != '' else '') + self.name_acc
 
     def name_locative(self, m="", f="", n="") -> str:
         w = {'m': m, 'f': f, 'n': n}[self.genus]
-        return (w + ' ' if w is not '' else '') + self.name_loc
+        return (w + ' ' if w != '' else '') + self.name_loc
 
     def in_name(self) -> str:
         return self.in_prep + ' ' + self.name_loc