code: def add_features(self, features):
          
          for feature in features:
              if isinstance(feature, basestring):
                  label = feature
                  value = None
              else:
                  label, value = feature
              self.add_feature(label, value)
docs: Add features to this namespace.
          features: An iterable of features.  A feature may be either
              1) A VW label (not containing characters from escape_dict.keys(),
                  unless 'escape' mode is on)
              2) A tuple (label, value) where value is any float