cleanup

Author: rickeylev

python/private/builders.bzl

@@ -185,8 +185,20 @@ def _is_runfiles(value):
     return type(value) == "runfiles"
 
 def _Optional(*initial):
+    """A wrapper for a re-assignable value that may or may not be set.
+
+    This allows structs to have attributes that aren't inherently mutable
+    and must be re-assigned to have their value updated.
+
+    Args:
+        *initial: A single vararg to be the initial value, or no args
+            to leave it unset.
+
+    Returns:
+        {type}`Optional`
+    """
     if len(initial) > 1:
-        fail("only one positional arg allowed")
+        fail("Only zero or one positional arg allowed")
 
     # buildifier: disable=uninitialized
     self = struct(