diff --git a/refex/python/matcher.py b/refex/python/matcher.py
index c8c90b1..e63e99f 100644
--- a/refex/python/matcher.py
+++ b/refex/python/matcher.py
@@ -182,9 +182,7 @@ def _coerce_list(values):
 _IS_SUBMATCHER_LIST_ATTRIB = __name__ + '._IS_SUBMATCHER_LIST_ATTRIB'
 
 
-def submatcher_attrib(
-    *args,
-    **kwargs: Any):  # TODO: make walk a kwarg when Py2 support is dropped.
+def submatcher_attrib(*args, walk: bool = True, **kwargs: Any):
   """Creates an attr.ib that is marked as a submatcher.
 
   This will cause the matcher to be automatically walked as part of the
@@ -199,15 +197,13 @@ def submatcher_attrib(
   Returns:
     An attr.ib()
   """
-  if kwargs.pop('walk', True):
+  if walk:
     kwargs.setdefault('metadata', {})[_IS_SUBMATCHER_ATTRIB] = True
   kwargs.setdefault('converter', coerce)
   return attr.ib(*args, **kwargs)
 
 
-def submatcher_list_attrib(
-    *args,
-    **kwargs: Any):  # TODO: make walk a kwarg when Py2 support is dropped.
+def submatcher_list_attrib(*args, walk: bool = True, **kwargs: Any):
   """Creates an attr.ib that is marked as an iterable of submatchers.
 
   This will cause the matcher to be automatically walked as part of the
@@ -222,7 +218,7 @@ def submatcher_list_attrib(
   Returns:
     An attr.ib()
   """
-  if kwargs.pop('walk', True):
+  if walk:
     kwargs.setdefault('metadata', {})[_IS_SUBMATCHER_LIST_ATTRIB] = True
   kwargs.setdefault('converter', _coerce_list)
   return attr.ib(*args, **kwargs)