code: def get_size(self, value=None):
          
          if value is None:
              value = self._value
  
          if hasattr(value, 'get_size'):
              return value.get_size()
  
          return len(self.pack(value))
docs: Return the size in bytes.
  
          Args:
              value (bytes): In structs, the user can assign other value instead
                  of this class' instance. Here, in such cases, ``self`` is a
                  class attribute of the struct.
  
          Returns:
              int: The address size in bytes.