code: def value(self, cell):
          
  
          if self._value is not None:
              return self._value(cell)
  
          else:
              return cell.value
docs: Extract the value of ``cell``, ready to be rendered.
  
          If this Column was instantiated with a ``value`` attribute, it
          is called here to provide the value. (For example, to provide a
          calculated value.) Otherwise, ``cell.value`` is returned.