Allow defining converter_pre and converter_post in templates

aleksis/apps/csv_import/field_types.py

@@ -32,22 +32,28 @@ class FieldType:
 
     @classmethod
     def get_converter(cls) -> Callable[[Any], Any]:
-        if not cls.converter:
-            return lambda val: val
-        else:
-            if isinstance(cls.converter, Sequence):
-                funcs = cls.converter
-            else:
-                funcs = [cls.converter]
-            funcs = [converter_registry.get_from_name(name) for name in funcs]
-
-            def _converter_chain(val: Any) -> Any:
-                new_val = val
-                for func in funcs:
-                    new_val = func(new_val)
-                return new_val
-
-            return _converter_chain
+        converters_pre = cls.get_args().get("converter_pre", [])
+        if isinstance(converters_pre, str):
+            converters_pre = [converters_pre]
+        converters_post = cls.get_args().get("converter_post", [])
+        if isinstance(converters_post, str):
+            converters_post = [converters_post]
+        converters = cls.converter
+        if converters is None:
+            converters = []
+        elif isinstance(converters, str):
+            converters = [converters]
+        converters = converters_pre + converters + converters_post
+
+        funcs = [converter_registry.get_from_name(name) for name in converters]
+
+        def _converter_chain(val: Any) -> Any:
+            new_val = val
+            for func in funcs:
+                new_val = func(new_val)
+            return new_val
+
+        return _converter_chain
 
     @classmethod
     def get_alternative(cls) -> Optional[str]: