MNT: change to immutable default value

tacaswell · tacaswell · commit 162e25b2ff17 · 2015-12-14T20:56:32.000-05:00
diff --git a/lib/matplotlib/cbook.py b/lib/matplotlib/cbook.py
@@ -1669,7 +1669,7 @@ class Grouper(object):
         False
 
     """
-    def __init__(self, init=[]):
+    def __init__(self, init=()):
         mapping = self._mapping = {}
         for x in init:
             mapping[ref(x)] = [ref(x)]
