Give some love to the VI mode.

Improve  #11329, still likely need a magic to make editign mode easier to toggle

IPython/terminal/interactiveshell.py

@@ -12,7 +12,7 b' from IPython.utils.terminal import toggle_set_term_title, set_term_title'
 from IPython.utils.process import abbrev_cwd
 from traitlets import (
     Bool, Unicode, Dict, Integer, observe, Instance, Type, default, Enum, Union,
-    Any,
+    Any, validate
 )
 
 from prompt_toolkit.enums import DEFAULT_BUFFER, EditingMode
@@ -131,6 +131,23 b' class TerminalInteractiveShell(InteractiveShell):'
         highlighting. To see available styles, run `pygmentize -L styles`."""
     ).tag(config=True)
 
+    @validate('editing_mode')
+    def _validate_editing_mode(self, proposal):
+        if proposal['value'].lower() == 'vim':
+            proposal['value']= 'vi'
+        elif proposal['value'].lower() == 'default':
+            proposal['value']= 'emacs'
+
+        if hasattr(EditingMode, proposal['value'].upper()):
+            return proposal['value'].lower()
+
+        return self.editing_mode
+
+
+    @observe('editing_mode')
+    def _editing_mode(self, change):
+        u_mode = change.new.upper()
+        self.pt_app.editing_mode = u_mode
 
     @observe('highlighting_style')
     @observe('colors')

IPython/terminal/prompts.py

@@ -13,8 +13,15 b' class Prompts(object):'
     def __init__(self, shell):
         self.shell = shell
 
+    def vi_mode(self):
+        if self.shell.pt_app.editing_mode == 'VI':
+            return '['+str(self.shell.pt_app.app.vi_state.input_mode)[3:6]+'] '
+        return ''
+
+
     def in_prompt_tokens(self):
         return [
+            (Token.Prompt, self.vi_mode() ),
             (Token.Prompt, 'In ['),
             (Token.PromptNum, str(self.shell.execution_count)),
             (Token.Prompt, ']: '),