Issue #27518: Merge from 3.5

1 files changed, 33 insertions, 0 deletions

diff --git a/Lib/idlelib/delegator.py b/Lib/idlelib/delegator.py
new file mode 100644
index 0000000000..dc2a1aaeea
--- /dev/null
+++ b/Lib/idlelib/delegator.py
@@ -0,0 +1,33 @@
+class Delegator:
+
+    def __init__(self, delegate=None):
+        self.delegate = delegate
+        self.__cache = set()
+        # Cache is used to only remove added attributes
+        # when changing the delegate.
+
+    def __getattr__(self, name):
+        attr = getattr(self.delegate, name) # May raise AttributeError
+        setattr(self, name, attr)
+        self.__cache.add(name)
+        return attr
+
+    def resetcache(self):
+        "Removes added attributes while leaving original attributes."
+        # Function is really about resetting delagator dict
+        # to original state.  Cache is just a means
+        for key in self.__cache:
+            try:
+                delattr(self, key)
+            except AttributeError:
+                pass
+        self.__cache.clear()
+
+    def setdelegate(self, delegate):
+        "Reset attributes and change delegate."
+        self.resetcache()
+        self.delegate = delegate
+
+if __name__ == '__main__':
+    from unittest import main
+    main('idlelib.idle_test.test_delegator', verbosity=2)