Adding decorator forms of interact. Yeah!

IPython/html/widgets/interaction.py

@@ -237,11 +237,29 b' def interactive(f, *args, **kwargs):'
 
     return container
 
-def interact(f, *args, **kwargs):
+def interact(*args, **kwargs):
     """Interact with a function using widgets."""
+    if args and callable(args[0]):
+        # This branch handles the cases:
+        # 1. interact(f, *args, **kwargs)
+        # 2. @interact
+        #    def f(*args, **kwargs):
+        #        ...
+        f = args[0]
+        w = interactive(f, *args[1:], **kwargs)
+        f.widget = w
+        display(w)
+    else:
+        # This branch handles the case:
+        # @interact(10, 20, a=30, b=40)
+        # def f(*args, **kwargs):
+        #     ...
+        def dec(f):
     w = interactive(f, *args, **kwargs)
     f.widget = w
     display(w)
+            return f
+        return dec
 
 def annotate(**kwargs):
     """Python 3 compatible function annotation for Python 2."""