code: def value_or_default(self, value):
          ''' Returns the given value or the specified default value for this
          field '''
          if value is None:
              if callable(self.default):
                  return self.default()
              else:
                  return self.default
  
          return valuf value_or_default(self, value):
          ''' Returns the given value or the specified default value for this
          field '''
          if value is None:
              if callable(self.default):
                  return self.default()
              else:
                  return self.default
  
          return value
docs: Returns the given value or the specified default value for this
          field