docs: def _validate_inputs(self, inputdict):
          """ Validate input links.
          """
          # Check code
          try:
              code = inputdict.pop(self.get_linkname('code'))
          except KeyError:
              raise InputValidationError("No code specified for this "
                                         "calculation")
  
          # Check input files
          try:
              surface_sample = inputdict.pop(self.get_linkname('surface_sample'))
              if not isinstance(surface_sample, SinglefileData):
                  raise InputValidationError(
                      "surface_sample not of type SinglefileData")
          except KeyError:
              raise InputValidationError(
                  "No input structure specified for calculation")
  
          try:
              cell = inputdict.pop(self.get_linkname('cell'))
              if not isinstance(cell, SinglefileData):
                  raise InputValidationError("cell not of type SinglefileData")
          except KeyError:
              raise InputValidationError(
                  "No input structure specified for calculation")
  
          # Check that nothing is left unparsed
          if inputdict:
              raise ValidationError("Unrecognized inputs: {}".format(inputdict))
  
          return code, surface_sample, cell