add silent kwarg to run_cell

This explicitly omits the actions described in the message spec:

* history/logger
* displayhook
* post-exec

IPython/core/interactiveshell.py

@@ -2429,7 +2429,7 b' class InteractiveShell(SingletonConfigurable, Magic):'
             self.showtraceback()
             warn('Unknown failure executing module: <%s>' % mod_name)
 
-    def run_cell(self, raw_cell, store_history=False):
+    def run_cell(self, raw_cell, store_history=False, silent=False):
         """Run a complete IPython cell.
 
         Parameters
@@ -2440,10 +2440,16 b' class InteractiveShell(SingletonConfigurable, Magic):'
           If True, the raw and translated cell will be stored in IPython's
           history. For user code calling back into IPython's machinery, this
           should be set to False.
+        silent : bool
+          If True, avoid side-effets, such as implicit displayhooks, history,
+          and logging.  silent=True forces store_history=False.
         """
         if (not raw_cell) or raw_cell.isspace():
             return
 
+        if silent:
+            store_history = False
+
         for line in raw_cell.splitlines():
             self.input_splitter.push(line)
         cell = self.input_splitter.source_reset()
@@ -2467,7 +2473,7 b' class InteractiveShell(SingletonConfigurable, Magic):'
             if store_history:
                 self.history_manager.store_inputs(self.execution_count,
                                                   cell, raw_cell)
-
+            if not silent:
             self.logger.log(cell, raw_cell)
 
             if not prefilter_failed:
@@ -2489,11 +2495,15 b' class InteractiveShell(SingletonConfigurable, Magic):'
                             self.execution_count += 1
                         return None
 
+                    interactivity = "none" if silent else "last_expr"
                     self.run_ast_nodes(code_ast.body, cell_name,
-                                       interactivity="last_expr")
+                                       interactivity=interactivity)
 
                     # Execute any registered post-execution functions.
-                    for func, status in self._post_execute.iteritems():
+                    # unless we are silent
+                    post_exec = [] if silent else self._post_execute.iteritems()
+                    
+                    for func, status in post_exec:
                         if self.disable_failing_post_execute and not status:
                             continue
                         try:

IPython/core/tests/test_interactiveshell.py

@@ -255,6 +255,61 b' class InteractiveShellTestCase(unittest.TestCase):'
         # ZeroDivisionError
         self.assertEqual(ip.var_expand(u"{1/0}"), u"{1/0}")
 
+    def test_silent_nopostexec(self):
+        """run_cell(silent=True) doesn't invoke post-exec funcs"""
+        ip = get_ipython()
+        
+        d = dict(called=False)
+        def set_called():
+            d['called'] = True
+        
+        ip.register_post_execute(set_called)
+        ip.run_cell("1", silent=True)
+        self.assertFalse(d['called'])
+        # double-check that non-silent exec did what we expected
+        # silent to avoid
+        ip.run_cell("1")
+        self.assertTrue(d['called'])
+        # remove post-exec
+        ip._post_execute.pop(set_called)
+    
+    def test_silent_noadvance(self):
+        """run_cell(silent=True) doesn't advance execution_count"""
+        ip = get_ipython()
+        
+        ec = ip.execution_count
+        # silent should force store_history=False
+        ip.run_cell("1", store_history=True, silent=True)
+        
+        self.assertEquals(ec, ip.execution_count)
+        # double-check that non-silent exec did what we expected
+        # silent to avoid
+        ip.run_cell("1", store_history=True)
+        self.assertEquals(ec+1, ip.execution_count)
+    
+    def test_silent_nodisplayhook(self):
+        """run_cell(silent=True) doesn't trigger displayhook"""
+        ip = get_ipython()
+        
+        d = dict(called=False)
+        
+        trap = ip.display_trap
+        save_hook = trap.hook
+        
+        def failing_hook(*args, **kwargs):
+            d['called'] = True
+        
+        try:
+            trap.hook = failing_hook
+            ip.run_cell("1", silent=True)
+            self.assertFalse(d['called'])
+            # double-check that non-silent exec did what we expected
+            # silent to avoid
+            ip.run_cell("1")
+            self.assertTrue(d['called'])
+        finally:
+            trap.hook = save_hook
+
     @skipif(sys.version_info[0] >= 3, "softspace removed in py3")
     def test_print_softspace(self):
         """Verify that softspace is handled correctly when executing multiple