code: def _toComparableValue(self, value):
          
          if hasattr(self.currentSortColumn, 'toComparableValue'):
              return self.currentSortColumn.toComparableValue(value)
          # Retrieve the location of the class's definition so that we can alert
          # the user as to where they need to insert their implementation.
          classDef = self.currentSortColumn.__class__
          filename = inspect.getsourcefile(classDef)
          lineno = inspect.findsource(classDef)[1]
          warnings.warn_explicit(
              "IColumn implementor " + qual(self.currentSortColumn.__class__) + " "
              "does not implement method toComparableValue.  This is required since "
              "Mantissa 0.6.6.",
              DeprecationWarning, filename, lineno)
          return value
docs: Trivial wrapper which takes into account the possibility that our sort
          column might not have defined the C{toComparableValue} method.
  
          This can probably serve as a good generic template for some
          infrastructure to deal with arbitrarily-potentially-missing methods
          from certain versions of interfaces, but we didn't take it any further
          than it needed to go for this system's fairly meagre requirements.
          *Please* feel free to refactor upwards as necessary.