lazy load widgets

Allow warnign to appear in notebook at the time widets get imported

IPython/kernel/zmq/ipkernel.py

@@ -5,7 +5,6 b' import sys'
 import traceback
 
 from IPython.core import release
-from IPython.html.widgets import Widget
 from IPython.utils.py3compat import builtin_mod, PY3
 from IPython.utils.tokenutil import token_at_cursor, line_at_cursor
 from IPython.utils.traitlets import Instance, Type, Any
@@ -16,6 +15,12 b' from .kernelbase import Kernel as KernelBase'
 from .serialize import serialize_object, unpack_apply_message
 from .zmqshell import ZMQInteractiveShell
 
+
+def lazy_import_handle_comm_opened(*args, **kwargs):
+    from IPython.html.widgets import Widget
+    Widget.handle_comm_opened(*args, **kwargs)
+
+
 class IPythonKernel(KernelBase):
     shell = Instance('IPython.core.interactiveshell.InteractiveShellABC')
     shell_class = Type(ZMQInteractiveShell)
@@ -59,7 +64,7 b' class IPythonKernel(KernelBase):'
 
         self.comm_manager = CommManager(shell=self.shell, parent=self, 
                                         kernel=self)
-        self.comm_manager.register_target('ipython.widget', Widget.handle_comm_opened)
+        self.comm_manager.register_target('ipython.widget', lazy_import_handle_comm_opened)
 
         self.shell.configurables.append(self.comm_manager)
         comm_msg_types = [ 'comm_open', 'comm_msg', 'comm_close' ]