[formatter] overload '.' operator

implement generic access of
* list items        (L[1]   -> L.1)
* dict vslues       (D[key] -> D.key)
* object attributes (O.attr -> O.attr)
in standard format strings

gallery_dl/formatter.py

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 
-# Copyright 2021-2025 Mike Fährmann
+# Copyright 2021-2026 Mike Fährmann
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 2 as
@@ -298,7 +298,7 @@ def parse_field_name(field_name):
 
     for is_attr, key in rest:
         if is_attr:
-            func = operator.attrgetter
+            func = _attrgetter
         else:
             func = operator.itemgetter
             try:
@@ -330,6 +330,22 @@ def _slice(indices):
     )
 
 
+def _attrgetter(key):
+
+    if key.isdecimal() or key[0] == "-":
+        try:
+            return operator.itemgetter(int(key))
+        except ValueError:
+            pass
+
+    def apply_key(obj):
+        try:
+            return obj[key]
+        except (TypeError, KeyError):
+            return getattr(obj, key)
+    return apply_key
+
+
 def _bytesgetter(slice):
 
     def apply_slice_bytes(obj):