From d2eff1832a13a3207b0f4f1bf23b1c74d90d4176 Mon Sep 17 00:00:00 2001
From: John Reese <john@noswap.com>
Date: Wed, 27 Jun 2018 13:37:50 -0700
Subject: [PATCH] bpo-33983: Make lib2to3.pytree.Base.children a list

The type difference between Base/Leaf (a tuple) and Node (a list)
makes it difficult to type check functions that take both, because
lists can be used in ways that tuples can't.
---
 Lib/lib2to3/pytree.py                                           | 2 +-
 .../next/Library/2018-06-27-13-55-05.bpo-33983.MRbonR.rst       | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2018-06-27-13-55-05.bpo-33983.MRbonR.rst

diff --git a/Lib/lib2to3/pytree.py b/Lib/lib2to3/pytree.py
index 2a6ef2ef5240a2..5a74f8e219c208 100644
--- a/Lib/lib2to3/pytree.py
+++ b/Lib/lib2to3/pytree.py
@@ -42,7 +42,7 @@ class Base(object):
     # Default values for instance variables
     type = None    # int: token number (< 256) or symbol number (>= 256)
     parent = None  # Parent node pointer, or None
-    children = ()  # Tuple of subnodes
+    children = []  # List of subnodes
     was_changed = False
     was_checked = False
 
diff --git a/Misc/NEWS.d/next/Library/2018-06-27-13-55-05.bpo-33983.MRbonR.rst b/Misc/NEWS.d/next/Library/2018-06-27-13-55-05.bpo-33983.MRbonR.rst
new file mode 100644
index 00000000000000..61ce89732f6aab
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-06-27-13-55-05.bpo-33983.MRbonR.rst
@@ -0,0 +1,2 @@
+:class:`lib2to3.pytree.Base` sets the `children` attribute to an empty
+list to be more consistent with :class:`lib2to3.pytree.Node`.