'Reload a configuration item from the configuration file.
Parameters
attr : str, optional
The name of the configuration parameter to reload.  If not
provided, reload all configuration parameters.'

def reload(self, attr=None):

    if (attr is not None):
        if hasattr(self, attr):
            return self.__class__.__dict__[attr].reload()
        raise AttributeError(u"No    configuration    parameter    '{0}'".format(attr))
    for item in six.itervalues(self.__class__.__dict__):
        if isinstance(item, ConfigItem):
            item.reload()
