diff --git a/bin/mn b/bin/mn
index d69b6b1..082a437 100755
--- a/bin/mn
+++ b/bin/mn
@@ -33,7 +33,7 @@ from mininet.nodelib import LinuxBridge
 from mininet.link import Link, TCLink, OVSLink
 from mininet.topo import SingleSwitchTopo, LinearTopo, SingleSwitchReversedTopo
 from mininet.topolib import TreeTopo, TorusTopo
-from mininet.util import customConstructor, splitArgs
+from mininet.util import customClass, specialClass, splitArgs
 from mininet.util import buildTopo
 
 from functools import partial
@@ -69,8 +69,8 @@ SWITCHES = { 'user': UserSwitch,
 
 HOSTDEF = 'proc'
 HOSTS = { 'proc': Host,
-          'rt': partial( CPULimitedHost, sched='rt' ),
-          'cfs': partial( CPULimitedHost, sched='cfs' ) }
+          'rt': specialClass( CPULimitedHost, defaults=dict( sched='rt' ) ),
+          'cfs': specialClass( CPULimitedHost, defaults=dict( sched='cfs' ) ) }
 
 CONTROLLERDEF = 'default'
 CONTROLLERS = { 'ref': Controller,
@@ -311,10 +311,10 @@ class MininetRunner( object ):
                                      self.options.switch )
 
         topo = buildTopo( TOPOS, self.options.topo )
-        switch = customConstructor( SWITCHES, self.options.switch )
-        host = customConstructor( HOSTS, self.options.host )
-        controller = customConstructor( CONTROLLERS, self.options.controller )
-        link = customConstructor( LINKS, self.options.link )
+        switch = customClass( SWITCHES, self.options.switch )
+        host = customClass( HOSTS, self.options.host )
+        controller = customClass( CONTROLLERS, self.options.controller )
+        link = customClass( LINKS, self.options.link )
 
         if self.validate:
             self.validate( self.options )
diff --git a/mininet/util.py b/mininet/util.py
index 517e0db..6755c6d 100644
--- a/mininet/util.py
+++ b/mininet/util.py
@@ -523,43 +523,56 @@ def splitArgs( argstr ):
         kwargs[ key ] = makeNumeric( val )
     return fn, args, kwargs
 
-def customConstructor( constructors, argStr ):
-    """Return custom constructor based on argStr
-    The args and key/val pairs in argsStr will be automatically applied
-    when the generated constructor is later used.
+def customClass( classes, argStr ):
+    """Return customized class based on argStr
+    The args and key/val pairs in argStr will be automatically applied
+    when the generated class is later used.
     """
-    cname, newargs, kwargs = splitArgs( argStr )
-    constructor = constructors.get( cname, None )
+    cname, args, kwargs = splitArgs( argStr )
+    cls = classes.get( cname, None )
 
-    if not constructor:
+    if not cname:
         raise Exception( "error: %s is unknown - please specify one of %s" %
                          ( cname, constructors.keys() ) )
+    if not args and not kwargs:
+        return cls
 
-    if not newargs and not kwargs:
-        return constructor
+    return specialClass( cls, append=args, defaults=kwargs )
 
-    if not isinstance( constructor, type ):
-        raise Exception( "error: invalid arguments %s" % argStr )
+def specialClass( cls, prepend=None, append=None,
+                  defaults=None, override=None ):
+    """Like functools.partial, but it returns a class
+       prepend: arguments to prepend to argument list
+       append: arguments to append to argument list
+       defaults: default values for keyword arguments
+       override: keyword arguments to override"""
 
-    # Return a customized subclass
-    cls = constructor
+    if prepend is None:
+        prepend = []
+
+    if append is None:
+        append = []
+
+    if defaults is None:
+        defaults = {}
+
+    if override is None:
+        override = {}
 
     class CustomClass( cls ):
-        "Customized subclass, useful for Node, Link, and other classes"
-        def __init__( self, name, *args, **params ):
-            params = params.copy()
-            params.update( kwargs )
-            if not newargs:
-                cls.__init__( self, name, *args, **params )
-                return
-            if args:
-                warn( 'warning: %s replacing %s with %s\n' %
-                      ( constructor, args, newargs ) )
-            cls.__init__( self, name, *newargs, **params )
+        "Customized subclass with preset args/params"
+        def __init__( self, *args, **params ):
+            newparams = defaults.copy()
+            newparams.update( params )
+            newparams.update( override )
+            cls.__init__( self, *( list( prepend ) + list( args ) +
+                                   list( append ) ),
+                          **newparams )
 
-    CustomClass.__name__ = '%s%s' % ( cls.__name__, kwargs )
+    CustomClass.__name__ = '%s%s' % ( cls.__name__, defaults )
     return CustomClass
 
+
 def buildTopo( topos, topoStr ):
     """Create topology from string with format (object, arg1, arg2,...).
     input topos is a dict of topo names to constructors, possibly w/args.