code: def define_attribute(self, name, atype, data=None):
          
          self.attributes.append(name)
          assert atype in TYPES, "Unknown type '%s'. Must be one of: %s" % (atype, ', '.join(TYPES),)
          self.attribute_types[name] = atype
          self.attribute_data[name] = data
docs: Define a new attribute. atype has to be one of 'integer', 'real', 'numeric', 'string', 'date' or 'nominal'.
          For nominal attributes, pass the possible values as data.
          For date attributes, pass the format as data.