fix callbacks/_callbacks typo

IPython/kernel/restarter.py

@@ -1,67 +1,67
 """A basic kernel monitor with autorestarting.
 
 This watches a kernel's state using KernelManager.is_alive and auto
 restarts the kernel if it dies.
 
 It is an incomplete base class, and must be subclassed.
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2013  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 
 from IPython.config.configurable import LoggingConfigurable
 from IPython.utils.traitlets import (
     Instance, Float, List,
 )
 
 #-----------------------------------------------------------------------------
 # Code
 #-----------------------------------------------------------------------------
 
 class KernelRestarter(LoggingConfigurable):
     """Monitor and autorestart a kernel."""
 
     kernel_manager = Instance('IPython.kernel.KernelManager')
 
     time_to_dead = Float(3.0, config=True,
         help="""Kernel heartbeat interval in seconds."""
     )
     _callbacks = List()
 
     def start(self):
         """Start the polling of the kernel."""
         raise NotImplementedError("Must be implemented in a subclass")
 
     def stop(self):
         """Stop the kernel polling."""
         raise NotImplementedError("Must be implemented in a subclass")
 
     def register_callback(self, f):
         """register a callback to fire"""
-        self.callbacks.append(f)
+        self._callbacks.append(f)
 
     def unregister_callback(self, f):
         try:
-            self.callbacks.remove(f)
+            self._callbacks.remove(f)
         except ValueError:
             pass
 
     def poll(self):
         self.log.debug('Polling kernel...')
         if not self.kernel_manager.is_alive():
             self.log.info('KernelRestarter: restarting kernel')
-            for callback in self.callbacks:
+            for callback in self._callbacks:
                 try:
                     callback()
                 except Exception as e:
                     self.log.error("Kernel restart callback %r failed", callback, exc_info=True)
             self.kernel_manager.restart_kernel(now=True)