custom keyboard interrupt handling in ask_yes_no

Sometimes, Ctrl-C just makes sense as an answer, and re-asking the
question is just frustrating. This changes makes it possible to break
out of the asking loop via Ctrl-C. This is particularly handy for asking
questions from the command line, where one expects Ctrl-c to be a sort
of "Cancel" operation, and is often functionally equivalent to "no"

IPython/utils/io.py

@@ -155,11 +155,13 b' class Tee(object):'
             self.close()
 
 
-def ask_yes_no(prompt,default=None):
+def ask_yes_no(prompt, default=None, interrupt=None):
     """Asks a question and returns a boolean (y/n) answer.
 
     If default is given (one of 'y','n'), it is used if the user input is
-    empty. Otherwise the question is repeated until an answer is given.
+    empty. If interrupt is given (one of 'y','n'), it is used if the user
+    presses Ctrl-C. Otherwise the question is repeated until an answer is
+    given.
 
     An EOF is treated as the default answer.  If there is no default, an
     exception is raised to prevent infinite loops.
@@ -174,7 +176,8 b' def ask_yes_no(prompt,default=None):'
             if not ans:  # response was an empty string
                 ans = default
         except KeyboardInterrupt:
-            pass
+            if interrupt:
+                ans = interrupt
         except EOFError:
             if default in answers.keys():
                 ans = default