MNT : make keys property return a copy

tacaswell · tacaswell · commit 105fcd68d626 · 2015-03-22T00:31:21.000-04:00
Don't open the chance for outside users to mess with contents of the
`_keys` attribute.
diff --git a/lib/matplotlib/cycler.py b/lib/matplotlib/cycler.py
@@ -55,7 +55,7 @@ def __init__(self, left, right=None, op=None):
 
     @property
     def keys(self):
-        return self._keys
+        return set(self._keys)
 
     def finite_iter(self):
         """
