Allow Embeded instances to raise on exit.

This is use full in case where an IPython embed instance is created in a loop:

    from IPython import embed
    while True:
        embed(header="You will be stuck there")

Now using `%raise_on_exist True` in an embeded shell allows the embeded
instannce to raise on exit.

Potential improvement would be flags to pass a custom exception type as
well as a custom message to raise.

Closes  #9149

IPython/terminal/embed.py

@@ -1,278 +1,317 b''
 # encoding: utf-8
 """
 An embedded IPython shell.
 """
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 from __future__ import with_statement
 from __future__ import print_function
 
 import sys
 import warnings
 
 from IPython.core import ultratb, compilerop
 from IPython.core.magic import Magics, magics_class, line_magic
 from IPython.core.interactiveshell import DummyMod
 from IPython.core.interactiveshell import InteractiveShell
 from IPython.terminal.interactiveshell import TerminalInteractiveShell
 from IPython.terminal.ipapp import load_default_config
 
 from traitlets import Bool, CBool, Unicode
 from IPython.utils.io import ask_yes_no
 
+class KillEmbeded(Exception):pass
 
 # This is an additional magic that is exposed in embedded shells.
 @magics_class
 class EmbeddedMagics(Magics):
 
     @line_magic
     def kill_embedded(self, parameter_s=''):
         """%kill_embedded : deactivate for good the current embedded IPython.
 
         This function (after asking for confirmation) sets an internal flag so
         that an embedded IPython will never activate again.  This is useful to
         permanently disable a shell that is being called inside a loop: once
         you've figured out what you needed from it, you may then kill it and
         the program will then continue to run without the interactive shell
         interfering again.
         """
 
         kill = ask_yes_no("Are you sure you want to kill this embedded instance "
                          "(y/n)? [y/N] ",'n')
         if kill:
             self.shell.embedded_active = False
             print ("This embedded IPython will not reactivate anymore "
                    "once you exit.")
 
+    @line_magic
+    def raise_on_exit(self, parameter_s=''):
+        """%raise_on_exit [True|False]: Make the current embeded kernel to raise an exception on exit.
+
+        You can change that again during current session by calling `%raise_on_exit` with `True`/`False` as parameter 
+
+        This function (after asking for confirmation) sets an internal flag so
+        that an embedded IPython will raise a `KillEmbeded` Exception on exit.  This is useful to
+        permanently exit a loop that create IPython embed instance.
+        """
+        parameter_s = parameter_s.strip().lower()
+
+        should_raise = None
+        if parameter_s in {'yes', 'raise', 'true', '1'}:
+            should_raise = True
+        elif parameter_s in {'no', 'false', '0', 'None'}:
+            should_raise = False
+        else:
+            if self.shell.should_raise :
+                print("The current embed instance will raise on exit, use `%raise_on_exit False` to disable")
+                return 
+            else:
+                print("The current embed instance will not raise on exit, use `%raise_on_exit True` to enable")
+                return 
+
+        if should_raise:
+            self.shell.should_raise = True
+            print ("This embedded IPython will raise while exiting.")
+        else :
+            self.shell.should_raise = False
+            print ("This embedded IPython will not raise while exiting.")
+
+
 
 class InteractiveShellEmbed(TerminalInteractiveShell):
 
     dummy_mode = Bool(False)
     exit_msg = Unicode('')
     embedded = CBool(True)
     embedded_active = CBool(True)
+    should_raise = CBool(False)
     # Like the base class display_banner is not configurable, but here it
     # is True by default.
     display_banner = CBool(True)
     exit_msg = Unicode()
     
 
     def __init__(self, **kw):
         
     
         if kw.get('user_global_ns', None) is not None:
             warnings.warn("user_global_ns has been replaced by user_module. The\
                            parameter will be ignored, and removed in IPython 5.0", DeprecationWarning)
 
         super(InteractiveShellEmbed,self).__init__(**kw)
 
         # don't use the ipython crash handler so that user exceptions aren't
         # trapped
         sys.excepthook = ultratb.FormattedTB(color_scheme=self.colors,
                                              mode=self.xmode,
                                              call_pdb=self.pdb)
 
     def init_sys_modules(self):
         pass
 
     def init_magics(self):
         super(InteractiveShellEmbed, self).init_magics()
         self.register_magics(EmbeddedMagics)
 
     def __call__(self, header='', local_ns=None, module=None, dummy=None,
                  stack_depth=1, global_ns=None, compile_flags=None):
         """Activate the interactive interpreter.
 
         __call__(self,header='',local_ns=None,module=None,dummy=None) -> Start
         the interpreter shell with the given local and global namespaces, and
         optionally print a header string at startup.
 
         The shell can be globally activated/deactivated using the
         dummy_mode attribute. This allows you to turn off a shell used
         for debugging globally.
 
         However, *each* time you call the shell you can override the current
         state of dummy_mode with the optional keyword parameter 'dummy'. For
         example, if you set dummy mode on with IPShell.dummy_mode = True, you
         can still have a specific call work by making it as IPShell(dummy=False).
         """
 
         # If the user has turned it off, go away
         if not self.embedded_active:
             return
 
         # Normal exits from interactive mode set this flag, so the shell can't
         # re-enter (it checks this variable at the start of interactive mode).
         self.exit_now = False
 
         # Allow the dummy parameter to override the global __dummy_mode
         if dummy or (dummy != 0 and self.dummy_mode):
             return
 
         if self.has_readline:
             self.set_readline_completer()
 
         # self.banner is auto computed
         if header:
             self.old_banner2 = self.banner2
             self.banner2 = self.banner2 + '\n' + header + '\n'
         else:
             self.old_banner2 = ''
 
         # Call the embedding code with a stack depth of 1 so it can skip over
         # our call and get the original caller's namespaces.
         self.mainloop(local_ns, module, stack_depth=stack_depth,
                       global_ns=global_ns, compile_flags=compile_flags)
 
         self.banner2 = self.old_banner2
 
         if self.exit_msg is not None:
             print(self.exit_msg)
 
+        if self.should_raise:
+            raise KillEmbeded('This instance has been marked as must raise on exit.')
+
+
     def mainloop(self, local_ns=None, module=None, stack_depth=0,
                  display_banner=None, global_ns=None, compile_flags=None):
         """Embeds IPython into a running python program.
 
         Parameters
         ----------
 
         local_ns, module
           Working local namespace (a dict) and module (a module or similar
           object). If given as None, they are automatically taken from the scope
           where the shell was called, so that program variables become visible.
 
         stack_depth : int
           How many levels in the stack to go to looking for namespaces (when
           local_ns or module is None). This allows an intermediate caller to
           make sure that this function gets the namespace from the intended
           level in the stack. By default (0) it will get its locals and globals
           from the immediate caller.
 
         compile_flags
           A bit field identifying the __future__ features
           that are enabled, as passed to the builtin :func:`compile` function.
           If given as None, they are automatically taken from the scope where
           the shell was called.
 
         """
         
         if (global_ns is not None) and (module is None):
             warnings.warn("global_ns is deprecated, and will be removed in IPython 5.0 use module instead.", DeprecationWarning)
             module = DummyMod()
             module.__dict__ = global_ns
 
         # Get locals and globals from caller
         if ((local_ns is None or module is None or compile_flags is None)
             and self.default_user_namespaces):
             call_frame = sys._getframe(stack_depth).f_back
 
             if local_ns is None:
                 local_ns = call_frame.f_locals
             if module is None:
                 global_ns = call_frame.f_globals
                 module = sys.modules[global_ns['__name__']]
             if compile_flags is None:
                 compile_flags = (call_frame.f_code.co_flags &
                                  compilerop.PyCF_MASK)
         
         # Save original namespace and module so we can restore them after 
         # embedding; otherwise the shell doesn't shut down correctly.
         orig_user_module = self.user_module
         orig_user_ns = self.user_ns
         orig_compile_flags = self.compile.flags
         
         # Update namespaces and fire up interpreter
         
         # The global one is easy, we can just throw it in
         if module is not None:
             self.user_module = module
 
         # But the user/local one is tricky: ipython needs it to store internal
         # data, but we also need the locals. We'll throw our hidden variables
         # like _ih and get_ipython() into the local namespace, but delete them
         # later.
         if local_ns is not None:
             reentrant_local_ns = {k: v for (k, v) in local_ns.items() if k not in self.user_ns_hidden.keys()}
             self.user_ns = reentrant_local_ns
             self.init_user_ns()
 
         # Compiler flags
         if compile_flags is not None:
             self.compile.flags = compile_flags
 
         # make sure the tab-completer has the correct frame information, so it
         # actually completes using the frame's locals/globals
         self.set_completer_frame()
 
         with self.builtin_trap, self.display_trap:
             self.interact(display_banner=display_banner)
         
         # now, purge out the local namespace of IPython's hidden variables.
         if local_ns is not None:
             local_ns.update({k: v for (k, v) in self.user_ns.items() if k not in self.user_ns_hidden.keys()})
 
         
         # Restore original namespace so shell can shut down when we exit.
         self.user_module = orig_user_module
         self.user_ns = orig_user_ns
         self.compile.flags = orig_compile_flags
 
 
 def embed(**kwargs):
     """Call this to embed IPython at the current point in your program.
 
     The first invocation of this will create an :class:`InteractiveShellEmbed`
     instance and then call it.  Consecutive calls just call the already
     created instance.
 
     If you don't want the kernel to initialize the namespace
     from the scope of the surrounding function,
     and/or you want to load full IPython configuration,
     you probably want `IPython.start_ipython()` instead.
 
     Here is a simple example::
 
         from IPython import embed
         a = 10
         b = 20
         embed(header='First time')
         c = 30
         d = 40
         embed()
 
     Full customization can be done by passing a :class:`Config` in as the
     config argument.
     """
     config = kwargs.get('config')
     header = kwargs.pop('header', u'')
     compile_flags = kwargs.pop('compile_flags', None)
     if config is None:
         config = load_default_config()
         config.InteractiveShellEmbed = config.TerminalInteractiveShell
         kwargs['config'] = config
     #save ps1/ps2 if defined
     ps1 = None
     ps2 = None
     try:
         ps1 = sys.ps1
         ps2 = sys.ps2
     except AttributeError:
         pass
     #save previous instance
     saved_shell_instance = InteractiveShell._instance
     if saved_shell_instance is not None:
         cls = type(saved_shell_instance)
         cls.clear_instance()
     shell = InteractiveShellEmbed.instance(**kwargs)
     shell(header=header, stack_depth=2, compile_flags=compile_flags)
     InteractiveShellEmbed.clear_instance()
     #restore previous instance
     if saved_shell_instance is not None:
         cls = type(saved_shell_instance)
         cls.clear_instance()
         for subclass in cls._walk_mro():
             subclass._instance = saved_shell_instance
     if ps1 is not None:
         sys.ps1 = ps1
         sys.ps2 = ps2