quiet error messages instead of tracebacks in %pylab/%gui

Including Terminal pylab, for unsupported backends

Also fix %pylab default in kernel to 'auto' like everywhere else, for uniformity.

IPython/frontend/terminal/interactiveshell.py

@@ -458,7 +458,11 b' class TerminalInteractiveShell(InteractiveShell):'
         # code in an empty namespace, and we update *both* user_ns and
         # user_ns_hidden with this information.
         ns = {}
-        gui = pylab_activate(ns, gui, import_all)
+        try:
+            gui = pylab_activate(ns, gui, import_all)
+        except KeyError:
+            error("Backend %r not supported" % gui)
+            return
         self.user_ns.update(ns)
         self.user_ns_hidden.update(ns)
         # Now we must activate the gui pylab wants to use, and fix %run to take

IPython/lib/pylabtools.py

@@ -196,7 +196,7 b' def find_gui_and_backend(gui=None):'
 
     import matplotlib
 
-    if gui:
+    if gui and gui != 'auto':
         # select backend based on requested gui
         backend = backends[gui]
     else:

IPython/zmq/ipkernel.py

@@ -740,8 +740,7 b' class IPKernelApp(KernelApp, InteractiveShellApp):'
         kernel_factory = Kernel
 
         if self.pylab:
-            key = None if self.pylab == 'auto' else self.pylab
-            gui, backend = pylabtools.find_gui_and_backend(key)
+            gui, backend = pylabtools.find_gui_and_backend(self.pylab)
 
         kernel = kernel_factory(config=self.config, session=self.session,
                                 shell_socket=self.shell_socket,

IPython/zmq/zmqshell.py

@@ -414,7 +414,12 b' class ZMQInteractiveShell(InteractiveShell):'
         from IPython.zmq.ipkernel import enable_gui
         opts, arg = self.parse_options(parameter_s, '')
         if arg=='': arg = None
-        return enable_gui(arg)
+        try:
+            enable_gui(arg)
+        except Exception as e:
+            # print simple error message, rather than traceback if we can't
+            # hook up the GUI
+            error(str(e))
 
     def enable_pylab(self, gui=None, import_all=True):
         """Activate pylab support at runtime.
@@ -440,13 +445,21 b' class ZMQInteractiveShell(InteractiveShell):'
         # code in an empty namespace, and we update *both* user_ns and
         # user_ns_hidden with this information.
         ns = {}
-        # override default to inline, from auto-detect
-        gui = pylabtools.pylab_activate(ns, gui or 'inline', import_all, self)
+        try:
+            gui = pylabtools.pylab_activate(ns, gui, import_all, self)
+        except KeyError:
+            error("Backend %r not supported" % gui)
+            return
         self.user_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)
+        try:
+            enable_gui(gui)
+        except Exception as e:
+            # print simple error message, rather than traceback if we can't
+            # hook up the GUI
+            error(str(e))
         self.magic_run = self._pylab_magic_run