allow using instance values in place of defaults in Configurable.class_get_help

IPython/config/configurable.py

@@ -149,34 +149,47 b' class Configurable(HasTraits):'
         self.config = newconfig
 
     @classmethod
-    def class_get_help(cls):
-        """Get the help string for this class in ReST format."""
+    def class_get_help(cls, inst=None):
+        """Get the help string for this class in ReST format.
+        
+        If `inst` is given, it's current trait values will be used in place of
+        class defaults.
+        """
+        assert inst is None or isinstance(inst, cls)
         cls_traits = cls.class_traits(config=True)
         final_help = []
         final_help.append(u'%s options' % cls.__name__)
         final_help.append(len(final_help[0])*u'-')
         for k,v in cls.class_traits(config=True).iteritems():
-            help = cls.class_get_trait_help(v)
+            help = cls.class_get_trait_help(v, inst)
             final_help.append(help)
         return '\n'.join(final_help)
 
     @classmethod
-    def class_get_trait_help(cls, trait):
-        """Get the help string for a single trait."""
+    def class_get_trait_help(cls, trait, inst=None):
+        """Get the help string for a single trait.
+        
+        If `inst` is given, it's current trait values will be used in place of
+        the class default.
+        """
+        assert inst is None or isinstance(inst, cls)
         lines = []
         header = "--%s.%s=<%s>" % (cls.__name__, trait.name, trait.__class__.__name__)
         lines.append(header)
-        try:
-            dvr = repr(trait.get_default_value())
-        except Exception:
-            dvr = None # ignore defaults we can't construct
-        if dvr is not None:
-            if len(dvr) > 64:
-                dvr = dvr[:61]+'...'
-            lines.append(indent('Default: %s'%dvr, 4))
+        if inst is not None:
+            lines.append(indent('Current: %r' % getattr(inst, trait.name), 4))
+        else:
+            try:
+                dvr = repr(trait.get_default_value())
+            except Exception:
+                dvr = None # ignore defaults we can't construct
+            if dvr is not None:
+                if len(dvr) > 64:
+                    dvr = dvr[:61]+'...'
+                lines.append(indent('Default: %s' % dvr, 4))
         if 'Enum' in trait.__class__.__name__:
             # include Enum choices
-            lines.append(indent('Choices: %r'%(trait.values,)))
+            lines.append(indent('Choices: %r' % (trait.values,)))
 
         help = trait.get_metadata('help')
         if help is not None:
@@ -185,9 +198,9 b' class Configurable(HasTraits):'
         return '\n'.join(lines)
 
     @classmethod
-    def class_print_help(cls):
+    def class_print_help(cls, inst=None):
         """Get the help string for a single trait and print it."""
-        print cls.class_get_help()
+        print cls.class_get_help(inst)
 
     @classmethod
     def class_config_section(cls):

IPython/config/tests/test_configurable.py

@@ -53,6 +53,15 b' mc_help=u"""MyConfigurable options'
     Default: 1.0
     The integer b."""
 
+mc_help_inst=u"""MyConfigurable options
+----------------------
+--MyConfigurable.a=<Int>
+    Current: 5
+    The integer a.
+--MyConfigurable.b=<Float>
+    Current: 4.0
+    The integer b."""
+
 class Foo(Configurable):
     a = Int(0, config=True, help="The integer a.")
     b = Unicode('nope', config=True)
@@ -139,6 +148,10 b' class TestConfigurable(TestCase):'
     def test_help(self):
         self.assertEquals(MyConfigurable.class_get_help(), mc_help)
 
+    def test_help_inst(self):
+        inst = MyConfigurable(a=5, b=4)
+        self.assertEquals(MyConfigurable.class_get_help(inst), mc_help_inst)
+
 
 class TestSingletonConfigurable(TestCase):