code: def _parse_index(self, v_name):
          
          i_start = i_end = i_stride = None
  
          # Start index
          self._update_tokens()
          try:
              i_start = int(self.token)
              self._update_tokens()
          except ValueError:
              if self.token in (',', ')'):
                  raise ValueError('{0} index cannot be empty.'.format(v_name))
              elif not self.token == ':':
                  raise
  
          # End index
          if self.token == ':':
              self._update_tokens()
              try:
                  i_end = 1 + int(self.token)
                  self._update_tokens()
              except ValueError:
                  if self.token == ':':
                      raise ValueError('{0} end index cannot be implicit '
                                       'when using stride.'.format(v_name))
                  elif self.token not in (',', ')'):
                      raise
          elif self.token in (',', ')'):
              # Replace index with single-index range
              if i_start:
                  i_end = 1 + i_start
  
          # Stride index
          if self.token == ':':
              self._update_tokens()
              try:
                  i_stride = int(self.token)
              except ValueError:
                  if self.token == ')':
                      raise ValueError('{0} stride index cannot be '
                                       'implicit.'.format(v_name))
                  else:
                      raise
  
              if i_stride == 0:
                  raise ValueError('{0} stride index cannot be zero.'
                                   ''.format(v_name))
  
              self._update_tokens()
  
          if self.token not in (',', ')'):
              raise ValueError('{0} index did not terminate '
                               'correctly.'.format(v_name))
  
          idx_triplet = (i_start, i_end, i_stride)
          return idx_triplet
docs: Parse Fortran vector indices into a tuple of Python indices.