Implement %doctest_mode magic in zmqshell with payload.

The frontend logic still needs to be written to toggle prompt displays
accordingly.

IPython/core/magic.py

@@ -3254,15 +3254,20 b' Defaulting color scheme to \'NoColor\'"""'
     def magic_doctest_mode(self,parameter_s=''):
         """Toggle doctest mode on and off.
 
-        This mode allows you to toggle the prompt behavior between normal
-        IPython prompts and ones that are as similar to the default IPython
-        interpreter as possible.
-
-        It also supports the pasting of code snippets that have leading '>>>'
-        and '...' prompts in them.  This means that you can paste doctests from
-        files or docstrings (even if they have leading whitespace), and the
-        code will execute correctly.  You can then use '%history -tn' to see
-        the translated history without line numbers; this will give you the
+        This mode is intended to make IPython behave as much as possible like a
+        plain Python shell, from the perspective of how its prompts, exceptions
+        and output look.  This makes it easy to copy and paste parts of a
+        session into doctests.  It does so by:
+
+        - Changing the prompts to the classic ``>>>`` ones.
+        - Changing the exception reporting mode to 'Plain'.
+        - Disabling pretty-printing of output.
+
+        Note that IPython also supports the pasting of code snippets that have
+        leading '>>>' and '...' prompts in them.  This means that you can paste
+        doctests from files or docstrings (even if they have leading
+        whitespace), and the code will execute correctly.  You can then use
+        '%history -t' to see the translated history; this will give you the
         input after removal of all the leading prompts and whitespace, which
         can be pasted back into an editor.
 
@@ -3308,7 +3313,6 b' Defaulting color scheme to \'NoColor\'"""'
             shell.pprint = False
             
             shell.magic_xmode('Plain')
-
         else:
             # turn off
             oc.prompt1.p_template = shell.prompt_in1
@@ -3329,8 +3333,8 b' Defaulting color scheme to \'NoColor\'"""'
 
         # Store new mode and inform
         dstore.mode = bool(1-int(mode))
-        print 'Doctest mode is:',
-        print ['OFF','ON'][dstore.mode]
+        mode_label = ['OFF','ON'][dstore.mode]
+        print 'Doctest mode is:', mode_label
 
     def magic_gui(self, parameter_s=''):
         """Enable or disable IPython GUI event loop integration.

IPython/zmq/zmqshell.py

@@ -86,6 +86,65 b' class ZMQInteractiveShell(InteractiveShell):'
         Term = IPython.utils.io.IOTerm()
         IPython.utils.io.Term = Term
 
+    def magic_doctest_mode(self,parameter_s=''):
+        """Toggle doctest mode on and off.
+
+        This mode is intended to make IPython behave as much as possible like a
+        plain Python shell, from the perspective of how its prompts, exceptions
+        and output look.  This makes it easy to copy and paste parts of a
+        session into doctests.  It does so by:
+
+        - Changing the prompts to the classic ``>>>`` ones.
+        - Changing the exception reporting mode to 'Plain'.
+        - Disabling pretty-printing of output.
+
+        Note that IPython also supports the pasting of code snippets that have
+        leading '>>>' and '...' prompts in them.  This means that you can paste
+        doctests from files or docstrings (even if they have leading
+        whitespace), and the code will execute correctly.  You can then use
+        '%history -t' to see the translated history; this will give you the
+        input after removal of all the leading prompts and whitespace, which
+        can be pasted back into an editor.
+
+        With these features, you can switch into this mode easily whenever you
+        need to do testing and changes to doctests, without having to leave
+        your existing IPython session.
+        """
+
+        from IPython.utils.ipstruct import Struct
+
+        # Shorthands
+        shell = self.shell
+        # dstore is a data store kept in the instance metadata bag to track any
+        # changes we make, so we can undo them later.
+        dstore = shell.meta.setdefault('doctest_mode', Struct())
+        save_dstore = dstore.setdefault
+
+        # save a few values we'll need to recover later
+        mode = save_dstore('mode', False)
+        save_dstore('rc_pprint', shell.pprint)
+        save_dstore('xmode', shell.InteractiveTB.mode)
+        
+        if mode == False:
+            # turn on
+            shell.pprint = False
+            shell.magic_xmode('Plain')
+        else:
+            # turn off
+            shell.pprint = dstore.rc_pprint
+            shell.magic_xmode(dstore.xmode)
+
+        # Store new mode and inform on console
+        dstore.mode = bool(1-int(mode))
+        mode_label = ['OFF','ON'][dstore.mode]
+        print('Doctest mode is:', mode_label)
+        
+        # Send the payload back so that clients can modify their prompt display
+        payload = dict(
+            source='IPython.zmq.zmqshell.ZMQInteractiveShell.magic_doctest_mode',
+            mode=dstore.mode)
+        self.payload_manager.write_payload(payload)
+
     def magic_edit(self,parameter_s='',last_call=['','']):
         """Bring up an editor and execute the resulting code.