[utils] Let traverse_obj accept functions as keys

yt_dlp/utils.py

@@ -6335,7 +6335,9 @@ def traverse_obj(
     ''' Traverse nested list/dict/tuple
     @param path_list        A list of paths which are checked one by one.
                             Each path is a list of keys where each key is a string,
-                            a tuple of strings or "...". When a tuple is given,
+                            a function, a tuple of strings or "...".
+                            When a fuction is given, it takes the key as argument and
+                            returns whether the key matches or not. When a tuple is given,
                             all the keys given in the tuple are traversed, and
                             "..." traverses all the keys in the object
     @param default          Default value to return
@@ -6368,6 +6370,18 @@ def traverse_obj(
                 _current_depth += 1
                 depth = max(depth, _current_depth)
                 return [_traverse_obj(inner_obj, path[i + 1:], _current_depth) for inner_obj in obj]
+            elif callable(key):
+                if isinstance(obj, (list, tuple, LazyList)):
+                    obj = enumerate(obj)
+                elif isinstance(obj, dict):
+                    obj = obj.items()
+                else:
+                    if not traverse_string:
+                        return None
+                    obj = str(obj)
+                _current_depth += 1
+                depth = max(depth, _current_depth)
+                return [_traverse_obj(v, path[i + 1:], _current_depth) for k, v in obj if key(k)]
             elif isinstance(obj, dict) and not (is_user_input and key == ':'):
                 obj = (obj.get(key) if casesense or (key in obj)
                        else next((v for k, v in obj.items() if _lower(k) == key), None))