More work to address review comments.

* Moved twisted import to top-level of :mod:`IPython.kernel.error` (r1333).
* Added docstring about :meth:`InteractiveShell.load_extension` returning
  whatever the return value of :func:`load_ipython_extension` is.
* Renamed the :attr:`user_config_ns` attribute to :attr:`user_ns_hidden` to
  better reflect what it does.
* Moved the ``%HOME`` to the end of home directory options attemped in
  :func:`IPython.utils.path.get_home_dir` on Windows.

IPython/core/iplib.py

@@ -833,7 +833,7 b' class InteractiveShell(Component, Magic):'
         # loaded at startup, so we can list later only variables defined in
         # actual interactive use.  Since it is always a subset of user_ns, it
         # doesn't need to be separately tracked in the ns_table.
-        self.user_config_ns = {}
+        self.user_ns_hidden = {}
 
         # A namespace to keep track of internal data structures to prevent
         # them from cluttering user-visible stuff.  Will be updated later
@@ -879,7 +879,7 b' class InteractiveShell(Component, Magic):'
         # Similarly, track all namespaces where references can be held and that
         # we can safely clear (so it can NOT include builtin).  This one can be
         # a simple list.
-        self.ns_refs_table = [ user_ns, user_global_ns, self.user_config_ns,
+        self.ns_refs_table = [ user_ns, user_global_ns, self.user_ns_hidden,
                                self.internal_ns, self._main_ns_cache ]
 
     def make_user_namespaces(self, user_ns=None, user_global_ns=None):
@@ -978,7 +978,7 b' class InteractiveShell(Component, Magic):'
         therm.
         """
         # This function works in two parts: first we put a few things in
-        # user_ns, and we sync that contents into user_config_ns so that these
+        # user_ns, and we sync that contents into user_ns_hidden so that these
         # initial variables aren't shown by %who.  After the sync, we add the
         # rest of what we *do* want the user to see with %who even on a new
         # session (probably nothing, so theye really only see their own stuff)
@@ -1018,9 +1018,9 b' class InteractiveShell(Component, Magic):'
         # Store myself as the public api!!!
         ns['get_ipython'] = self.get_ipython
 
-        # Sync what we've added so far to user_config_ns so these aren't seen
+        # Sync what we've added so far to user_ns_hidden so these aren't seen
         # by %who
-        self.user_config_ns.update(ns)
+        self.user_ns_hidden.update(ns)
 
         # Anything put into ns now would show up in %who.  Think twice before
         # putting anything here, as we really want %who to show the user their
@@ -1093,7 +1093,7 b' class InteractiveShell(Component, Magic):'
         self.user_ns.update(vdict)
 
         # And configure interactive visibility
-        config_ns = self.user_config_ns
+        config_ns = self.user_ns_hidden
         if interactive:
             for name, val in vdict.iteritems():
                 config_ns.pop(name, None)
@@ -2360,6 +2360,9 b' class InteractiveShell(Component, Magic):'
         to make it easy to write extensions, you can also put your extensions
         in ``os.path.join(self.ipython_dir, 'extensions')``.  This directory
         is added to ``sys.path`` automatically.
+
+        If :func:`load_ipython_extension` returns anything, this function
+        will return that object.
         """
         from IPython.utils.syspathcontext import prepended_to_syspath
 
@@ -2504,11 +2507,11 b' class InteractiveShell(Component, Magic):'
         # We want to prevent the loading of pylab to pollute the user's
         # namespace as shown by the %who* magics, so we execute the activation
         # code in an empty namespace, and we update *both* user_ns and
-        # user_config_ns with this information.
+        # user_ns_hidden with this information.
         ns = {}
         gui = pylab_activate(ns, gui)
         self.user_ns.update(ns)
-        self.user_config_ns.update(ns)
+        self.user_ns_hidden.update(ns)
         # Now we must activate the gui pylab wants to use, and fix %run to take
         # plot updates into account
         enable_gui(gui)

IPython/core/magic.py

@@ -886,10 +886,10 b' Currently the magic system has the following functions:\\n"""'
 
         user_ns = self.shell.user_ns
         internal_ns = self.shell.internal_ns
-        user_config_ns = self.shell.user_config_ns
+        user_ns_hidden = self.shell.user_ns_hidden
         out = [ i for i in user_ns
                 if not i.startswith('_') \
-                and not (i in internal_ns or i in user_config_ns) ]
+                and not (i in internal_ns or i in user_ns_hidden) ]
 
         typelist = parameter_s.split()
         if typelist:

IPython/core/tests/test_iplib.py

@@ -30,9 +30,9 b' ip = get_ipython()'
 @dec.parametric
 def test_reset():
     """reset must clear most namespaces."""
-    # The number of variables in the private user_config_ns is not zero, but it
+    # The number of variables in the private user_ns_hidden is not zero, but it
     # should be constant regardless of what we do
-    nvars_config_ns = len(ip.user_config_ns)
+    nvars_config_ns = len(ip.user_ns_hidden)
 
     # Check that reset runs without error
     ip.reset()
@@ -51,7 +51,7 b' def test_reset():'
     for ns in ip.ns_refs_table:
         if ns is ip.user_ns:
             nvars_expected = nvars_user_ns
-        elif ns is ip.user_config_ns:
+        elif ns is ip.user_ns_hidden:
             nvars_expected = nvars_config_ns
         else:
             nvars_expected = 0

IPython/kernel/error.py

@@ -18,6 +18,8 b' __test__ = {}'
 # Imports
 #-------------------------------------------------------------------------------
 
+from twisted.python import failure
+
 from IPython.kernel.core import error
 
 #-------------------------------------------------------------------------------
@@ -27,6 +29,7 b' from IPython.kernel.core import error'
 class KernelError(error.IPythonError):
     pass
 
+
 class NotDefined(KernelError):
     def __init__(self, name):
         self.name = name
@@ -37,78 +40,102 b' class NotDefined(KernelError):'
     
     __str__ = __repr__
 
+
 class QueueCleared(KernelError):
     pass
 
+
 class IdInUse(KernelError):
     pass
 
+
 class ProtocolError(KernelError):
     pass
 
+
 class ConnectionError(KernelError):
     pass
 
+
 class InvalidEngineID(KernelError):
     pass
-    
+
+
 class NoEnginesRegistered(KernelError):
     pass
-    
+
+
 class InvalidClientID(KernelError):
     pass
-    
+
+
 class InvalidDeferredID(KernelError):
     pass
-    
+
+
 class SerializationError(KernelError):
     pass
-    
+
+
 class MessageSizeError(KernelError):
     pass
-    
+
+
 class PBMessageSizeError(MessageSizeError):
     pass
-    
+
+
 class ResultNotCompleted(KernelError):
     pass
-    
+
+
 class ResultAlreadyRetrieved(KernelError):
     pass
-    
+
 class ClientError(KernelError):
     pass
 
+
 class TaskAborted(KernelError):
     pass
 
+
 class TaskTimeout(KernelError):
     pass
 
+
 class NotAPendingResult(KernelError):
     pass
 
+
 class UnpickleableException(KernelError):
     pass
 
+
 class AbortedPendingDeferredError(KernelError):
     pass
 
+
 class InvalidProperty(KernelError):
     pass
 
+
 class MissingBlockArgument(KernelError):
     pass
 
+
 class StopLocalExecution(KernelError):
     pass
 
+
 class SecurityError(KernelError):
     pass
 
+
 class FileTimeoutError(KernelError):
     pass
 
+
 class TaskRejectError(KernelError):
     """Exception to raise when a task should be rejected by an engine.
     
@@ -123,6 +150,7 b' class TaskRejectError(KernelError):'
     properties don't have to be managed or tested by the controller.
     """
 
+
 class CompositeError(KernelError):
     def __init__(self, message, elist):
         Exception.__init__(self, *(message, elist))
@@ -177,9 +205,8 b' class CompositeError(KernelError):'
         else:
             raise et, ev, etb
 
-def collect_exceptions(rlist, method):
-    from twisted.python import failure
 
+def collect_exceptions(rlist, method):
     elist = []
     for r in rlist:
         if isinstance(r, failure.Failure):

IPython/utils/path.py

@@ -188,12 +188,7 b' def get_home_dir():'
         # is needed when running IPython on cluster where all paths have to 
         # be UNC.
         try:
-            # A user with a lot of unix tools in win32 may have defined $HOME,
-            # honor it if it exists, but otherwise let the more typical
-            # %HOMESHARE% variable be used.
-            homedir = env.get('HOME')
-            if homedir is None:
-                homedir = env['HOMESHARE']
+            homedir = env['HOMESHARE']
         except KeyError:
             pass
         else:
@@ -233,6 +228,16 b' def get_home_dir():'
             if isdir(homedir):
                 return homedir.decode(sys.getfilesystemencoding())
 
+        # A user with a lot of unix tools in win32 may have defined $HOME.
+        # Try this as a last ditch option.
+        try:
+            homedir = env['HOME']
+        except KeyError:
+            pass
+        else:
+            if isdir(homedir):
+                return homedir.decode(sys.getfilesystemencoding())
+
         # If all else fails, raise HomeDirError
         raise HomeDirError('No valid home directory could be found')
     elif os.name == 'dos':