def _config_changed(self, name, old, new):
        """Update all the class traits having ``config=True`` as metadata.

        For any class trait with a ``config`` metadata attribute that is
        ``True``, we update the trait with the value of the corresponding
        config entry.
        """
        # Get all traits with a config metadata entry that is True
        traits = self.traits(config=True)

        # We auto-load config section for this class as well as any parent
        # classes that are Configurable subclasses.  This starts with Configurable
        # and works down the mro loading the config for each section.
        section_names = [cls.__name__ for cls in \
            reversed(self.__class__.__mro__) if
            issubclass(cls, Configurable) and issubclass(self.__class__, cls)]

        for sname in section_names:
            # Don't do a blind getattr as that would cause the config to
            # dynamically create the section with name self.__class__.__name__.
            if new._has_section(sname):
                my_config = new[sname]
                for k, v in traits.iteritems():
                    # Don't allow traitlets with config=True to start with
                    # uppercase.  Otherwise, they are confused with Config
                    # subsections.  But, developers shouldn't have uppercase
                    # attributes anyways! (PEP 6)
                    if k[0].upper()==k[0] and not k.startswith('_'):
                        raise ConfigurableError('Configurable traitlets with '
                        'config=True must start with a lowercase so they are '
                        'not confused with Config subsections: %s.%s' % \
                        (self.__class__.__name__, k))
                    try:
                        # Here we grab the value from the config
                        # If k has the naming convention of a config
                        # section, it will be auto created.
                        config_value = my_config[k]
                    except KeyError:
                        pass
                    else:
                        # print "Setting %s.%s from %s.%s=%r" % \
                        #     (self.__class__.__name__,k,sname,k,config_value)
                        # We have to do a deepcopy here if we don't deepcopy the entire
                        # config object. If we don't, a mutable config_value will be
                        # shared by all instances, effectively making it a class attribute.
                        setattr(self, k, deepcopy(config_value))
Update all the class traits having ``config=True`` as metadata.

        For any class trait with a ``config`` metadata attribute that is
        ``True``, we update the trait with the value of the corresponding
        config entry.