code: def is_valid(self, name, value):
          
          if name not in self.header_types:
              return False
          t = self.header_types[name]
          if t == ATTR_TYPE_DISCRETE:
              return isinstance(value, int)
          elif t == ATTR_TYPE_CONTINUOUS:
              return isinstance(value, (float, Decimal))
          return True
docs: Returns true if the given value matches the type for the given name
          according to the schema.
          Returns false otherwise.