Implement deletion mechanism to remove references held by IPython behind the scenes. Exposed to the user as %xdel.

IPython/core/interactiveshell.py

@@ -1079,7 +1079,49 b' class InteractiveShell(Configurable, Magic):'
         
         # Clear out the namespace from the last %run
         self.new_main_mod()
-
+    
+    def del_var(self, varname, by_name=False):
+        """Delete a variable from the various namespaces, so that, as
+        far as possible, we're not keeping any hidden references to it.
+        
+        Parameters
+        ----------
+        varname : str
+            The name of the variable to delete.
+        by_name : bool
+            If True, delete variables with the given name in each
+            namespace. If False (default), find the variable in the user
+            namespace, and delete references to it.
+        """
+        if varname in ('__builtin__', '__builtins__'):
+            raise ValueError("Refusing to delete %s" % varname)
+        ns_refs = self.ns_refs_table + [self.user_ns,
+                self.user_global_ns, self._user_main_module.__dict__] +\
+                self._main_ns_cache.values()
+        
+        if by_name:                    # Delete by name
+            for ns in ns_refs:
+                try:
+                    del ns[varname]
+                except KeyError:
+                    pass
+        else:                         # Delete by object
+            try:
+                obj = self.user_ns[varname]
+            except KeyError:
+                raise NameError("name '%s' is not defined" % varname)
+            # Also check in output history
+            ns_refs.append(self.history_manager.output_hist)
+            for ns in ns_refs:
+                to_delete = [n for n, o in ns.iteritems() if o is obj]
+                for name in to_delete:
+                    del ns[name]
+                    
+            # displayhook keeps extra references, but not in a dictionary
+            for name in ('_', '__', '___'):
+                if getattr(self.displayhook, name) is obj:
+                    setattr(self.displayhook, name, None)
+    
     def reset_selective(self, regex=None):
         """Clear selective variables from internal namespaces based on a
         specified regular expression.

IPython/core/magic.py

@@ -1081,7 +1081,24 b' Currently the magic system has the following functions:\\n"""'
                 raise TypeError('regex must be a string or compiled pattern')
             for i in self.magic_who_ls():
                 if m.search(i): 
-                    del(user_ns[i])        
+                    del(user_ns[i])
+                    
+    def magic_xdel(self, parameter_s=''):
+        """Delete a variable, trying to clear it from anywhere that
+        IPython's machinery has references to it. By default, this uses
+        the identity of the named object in the user namespace to remove
+        references held under other names. The object is also removed
+        from the output history.
+        
+        Options
+          -n : Delete the specified name from all namespaces, without
+          checking their identity.
+        """
+        opts, varname = self.parse_options(parameter_s,'n')
+        try:
+            self.shell.del_var(varname, ('n' in opts))
+        except (NameError, ValueError) as e:
+            print type(e).__name__ +": "+ str(e)
         
     def magic_logstart(self,parameter_s=''):
         """Start logging anywhere in a session.