[formatter] implement 'X' format specifier (#5770)

gallery_dl/formatter.py

@@ -423,6 +423,19 @@ def _parse_sort(format_spec, default):
         return sort_asc
 
 
+def _parse_limit(format_spec, default):
+    limit, hint, format_spec = format_spec.split(_SEPARATOR, 2)
+    limit = int(limit[1:])
+    limit_hint = limit - len(hint)
+    fmt = _build_format_func(format_spec, default)
+
+    def apply_limit(obj):
+        if len(obj) > limit:
+            obj = obj[:limit_hint] + hint
+        return fmt(obj)
+    return apply_limit
+
+
 def _default_format(format_spec, default):
     def wrap(obj):
         return format(obj, format_spec)
@@ -469,9 +482,10 @@ _FORMAT_SPECIFIERS = {
     "[": _parse_slice,
     "C": _parse_conversion,
     "D": _parse_datetime,
-    "L": _parse_maxlen,
     "J": _parse_join,
+    "L": _parse_maxlen,
     "O": _parse_offset,
     "R": _parse_replace,
     "S": _parse_sort,
+    "X": _parse_limit,
 }