Address comments

* Use 'cls' when calling class or static methods from class method
* Create submethod for 'get_locations'

transmogrifier/sources/xml/marc.py

@@ -731,7 +731,7 @@ def _get_language_names(
             language_name
             for language_code in list(dict.fromkeys(language_codes))
             if (
-                language_name := Marc.loc_crosswalk_code_to_name(
+                language_name := cls.loc_crosswalk_code_to_name(
                     language_code,
                     cls.language_code_crosswalk,
                     cls.get_source_record_id(source_record),
@@ -826,21 +826,9 @@ def get_locations(cls, source_record: Tag) -> list[timdex.Location] | None:
                 "kind": "Hierarchical Place Name",
             },
         ]
-
         # get locations (place of publication) from control field 008/15-17
-        if (
-            fixed_location_code := cls._get_control_field(source_record)[15:18].strip()
-        ) and (
-            location_name := Marc.loc_crosswalk_code_to_name(
-                code=fixed_location_code,
-                crosswalk=cls.country_code_crosswalk,
-                record_id=cls.get_source_record_id(source_record),
-                code_type="country",
-            )
-        ):
-            locations.append(
-                timdex.Location(value=location_name, kind="Place of Publication")
-            )
+        if place_of_publication := cls._get_location_publication(source_record):
+            locations.append(place_of_publication)
 
         # get locations from data fields
         for location_marc_field in location_marc_fields:
@@ -866,6 +854,21 @@ def get_locations(cls, source_record: Tag) -> list[timdex.Location] | None:
             )
         return locations or None
 
+    @classmethod
+    def _get_location_publication(cls, source_record: Tag) -> timdex.Location | None:
+        if (
+            fixed_location_code := cls._get_control_field(source_record)[15:18].strip()
+        ) and (
+            location_name := cls.loc_crosswalk_code_to_name(
+                code=fixed_location_code,
+                crosswalk=cls.country_code_crosswalk,
+                record_id=cls.get_source_record_id(source_record),
+                code_type="country",
+            )
+        ):
+            return timdex.Location(value=location_name, kind="Place of Publication")
+        return None
+
     @classmethod
     def get_notes(cls, source_record: Tag) -> list[timdex.Note] | None:
         notes = []