gh-82116: add comment explaining use of list(scandir_it) in pathlib. (GH-94939)

Automerge-Triggered-By: GH:brettcannon

Author: barneygale

Lib/pathlib.py

@@ -299,6 +299,8 @@ def __init__(self, pat, child_parts, flavour):
 
     def _select_from(self, parent_path, is_dir, exists, scandir):
         try:
+            # We must close the scandir() object before proceeding to
+            # avoid exhausting file descriptors when globbing deep trees.
             with scandir(parent_path) as scandir_it:
                 entries = list(scandir_it)
             for entry in entries:
@@ -330,6 +332,8 @@ def __init__(self, pat, child_parts, flavour):
     def _iterate_directories(self, parent_path, is_dir, scandir):
         yield parent_path
         try:
+            # We must close the scandir() object before proceeding to
+            # avoid exhausting file descriptors when globbing deep trees.
             with scandir(parent_path) as scandir_it:
                 entries = list(scandir_it)
             for entry in entries: