Make style and layout dynamic.

Recompute the lout of the application when the number of required line
for the completion change.

Use Prompt Toolkit to provide Dynamic colors when using the `config`
Magic.

IPython/terminal/ptshell.py

@@ -19,7 +19,7 b' from prompt_toolkit.completion import Completer, Completion'
 from prompt_toolkit.enums import DEFAULT_BUFFER, SEARCH_BUFFER
 from prompt_toolkit.filters import HasFocus, HasSelection, Condition
 from prompt_toolkit.history import InMemoryHistory
-from prompt_toolkit.shortcuts import create_prompt_application, create_eventloop
+from prompt_toolkit.shortcuts import create_prompt_application, create_eventloop, create_prompt_layout
 from prompt_toolkit.interface import CommandLineInterface
 from prompt_toolkit.key_binding.manager import KeyBindingManager
 from prompt_toolkit.key_binding.vi_state import InputMode
@@ -27,9 +27,9 b' from prompt_toolkit.key_binding.bindings.vi import ViStateFilter'
 from prompt_toolkit.keys import Keys
 from prompt_toolkit.layout.lexers import Lexer
 from prompt_toolkit.layout.lexers import PygmentsLexer
-from prompt_toolkit.styles import PygmentsStyle
+from prompt_toolkit.styles import PygmentsStyle, DynamicStyle
 
-from pygments.styles import get_style_by_name
+from pygments.styles import get_style_by_name, get_all_styles
 from pygments.lexers import Python3Lexer, BashLexer, PythonLexer
 from pygments.token import Token
 
@@ -92,6 +92,9 b' class TerminalInteractiveShell(InteractiveShell):'
     space_for_menu = Integer(6, config=True, help='space at the bottom of the screen to reserve for'
                                                   'the completion menu')
 
+    def _space_for_menu_changed(self, old, new):
+        self.relayout()
+
     pt_cli = None
 
     autoedit_syntax = CBool(False, config=True,
@@ -111,10 +114,13 b' class TerminalInteractiveShell(InteractiveShell):'
         help="Enable mouse support in the prompt"
     )
 
-    highlighting_style = Unicode('', config=True,
-        help="The name of a Pygments style to use for syntax highlighting"
+    highlighting_style = Unicode('default', config=True,
+            help="The name of a Pygments style to use for syntax highlighting: \n %s" % ', '.join(get_all_styles())
     )
 
+    def _highlighting_style_changed(self, old, new):
+        self._style = self._make_style_from_name(self.highlighting_style)
+
     highlighting_style_overrides = Dict(config=True,
         help="Override highlighting format for specific tokens"
     )
@@ -223,13 +229,33 b' class TerminalInteractiveShell(InteractiveShell):'
             if cell and (cell != last_cell):
                 history.append(cell)
 
+        self._style = self._make_style_from_name(self.highlighting_style)
+        style = DynamicStyle(lambda: self._style)
+
+        self._app = create_prompt_application(
+                            key_bindings_registry=kbmanager.registry,
+                            history=history,
+                            completer=IPythonPTCompleter(self.Completer),
+                            enable_history_search=True,
+                            style=style,
+                            mouse_support=self.mouse_support,
+                            **self._layout_options()
+        )
+        self.pt_cli = CommandLineInterface(self._app,
+                           eventloop=create_eventloop(self.inputhook))
+
+    def _make_style_from_name(self, name):
+        """
+        Small wrapper that make an IPython compatible style from a style name
+
+        We need that to add style for prompt ... etc. 
+        """
+        style_cls = get_style_by_name(name)
         style_overrides = {
             Token.Prompt: '#009900',
             Token.PromptNum: '#00ff00 bold',
         }
-        if self.highlighting_style:
-            style_cls = get_style_by_name(self.highlighting_style)
-        else:
+        if name is 'default':
             style_cls = get_style_by_name('default')
             # The default theme needs to be visible on both a dark background
             # and a light background, because we can't tell what the terminal
@@ -246,21 +272,27 b' class TerminalInteractiveShell(InteractiveShell):'
         style = PygmentsStyle.from_defaults(pygments_style_cls=style_cls,
                                             style_dict=style_overrides)
 
-        app = create_prompt_application(multiline=True,
-                            lexer=IPythonPTLexer(),
-                            get_prompt_tokens=self.get_prompt_tokens,
-                            get_continuation_tokens=self.get_continuation_tokens,
-                            key_bindings_registry=kbmanager.registry,
-                            history=history,
-                            completer=IPythonPTCompleter(self.Completer),
-                            enable_history_search=True,
-                            style=style,
-                            mouse_support=self.mouse_support,
-                            reserve_space_for_menu=self.space_for_menu,
-        )
+        return style
 
-        self.pt_cli = CommandLineInterface(app,
-                           eventloop=create_eventloop(self.inputhook))
+    def _layout_options(self):
+        """
+        Return the current layout option for the current Terminal InteractiveShell
+        """
+        return {
+                'lexer':IPythonPTLexer(),
+                'reserve_space_for_menu':self.space_for_menu,
+                'get_prompt_tokens':self.get_prompt_tokens,
+                'get_continuation_tokens':self.get_continuation_tokens,
+                'multiline':False,
+                }
+
+
+    def _relayout(self):
+        """
+        Ask for a re computation of the application layout, if for example ,
+        some configuration options have changed.
+        """
+        self._app.layout = create_prompt_layout(**self._layout_options())
 
     def prompt_for_code(self):
         document = self.pt_cli.run(pre_run=self.pre_prompt)