Implement key changing

Author: WeatherGod

cycler.py

@@ -138,6 +138,46 @@ def keys(self):
         """
         return set(self._keys)
 
+    def key_change(self, old, new):
+        """
+        Change a key in this cycler to a new name.
+        Modification is performed in-place.
+
+        Does nothing if the old key is the same as the new key.
+        Raises a ValueError if the new key is already a key.
+        Raises a KeyError if the old key isn't a key.
+
+        """
+        if old == new:
+            return
+        if new in self._keys:
+            raise ValueError("Can't replace %s with %s, %s is already a key" %
+                             (old, new, new))
+        if old not in self._keys:
+            raise KeyError("Can't replace %s with %s, %s is not a key" %
+                           (old, new, old))
+
+        self._keys.remove(old)
+        self._keys.add(new)
+
+        if self._right is not None and old in self._right.keys:
+            self._right.key_change(old, new)
+        elif self._left is not None:
+            if isinstance(self._left, Cycler):
+                self._left.key_change(old, new)
+            else:
+                Cycler._key_change(iter(self._left), old, new)
+
+    @staticmethod
+    def _key_change(itr, old, new):
+        entry = six.next(itr)
+        if old in entry:
+            entry[new] = entry[old]
+            del entry[old]
+            for entry in itr:
+                entry[new] = entry[old]
+                del entry[old]
+
     def _compose(self):
         """
         Compose the 'left' and 'right' components of this cycle

test_cycler.py

@@ -216,6 +216,32 @@ def test_copying():
     assert_equal(c3, cycler('foo', [['y', 'g', 'blue'], ['b', 'k']]))
 
 
+def test_keychange():
+    c1 = cycler('c', 'rgb')
+    c2 = cycler('lw', [1, 2, 3])
+    c3 = cycler('ec', 'yk')
+
+    c3.key_change('ec', 'edgecolor')
+    assert_equal(c3, cycler('edgecolor', c3))
+
+    c = c1 + c2
+    c.key_change('lw', 'linewidth')
+    assert_equal(c, c1 + cycler('linewidth', c2))
+
+    c = (c1 + c2) * c3
+    c.key_change('c', 'color')
+    assert_equal(c, (cycler('color', c1) + c2) * c3)
+
+    # Perfectly fine, it is a no-op
+    c.key_change('color', 'color')
+    assert_equal(c, (cycler('color', c1) + c2) * c3)
+
+    # Can't change a key to one that is already in there
+    assert_raises(ValueError, Cycler.key_change, c, 'color', 'linewidth')
+    # Can't change a key you don't have
+    assert_raises(KeyError, Cycler.key_change, c, 'c', 'foobar')
+
+
 def _eq_test_helper(a, b, res):
     if res:
         assert_equal(a, b)