code: def dg_value(self, descriptor_group):
          
          for p in self.descriptors:
              if p in descriptor_group:
                  return descriptor_group.canonical_value(p)
          return None
docs: Return the canonical value of a descriptor of the character,
          provided it is present in the given descriptor group.
  
          If not present, return ``None``.
  
          :param IPADescriptorGroup descriptor_group: the descriptor group to be checked against
          :rtype: str