code: def ensure_hash(self):
          
          fields = self.table.fieldnames
          if 'template_hash' in fields:
              return
  
          # The fields to use in making a template hash
          hash_fields = ['mass1', 'mass2', 'inclination',
                         'spin1x', 'spin1y', 'spin1z',
                         'spin2x', 'spin2y', 'spin2z',]
  
          fields = [f for f in hash_fields if f in fields]
          template_hash = np.array([hash(v) for v in zip(*[self.table[p]
                                    for p in fields])])
          self.table = self.table.add_fields(template_hash, 'template_hash')
docs: Ensure that there is a correctly populated template_hash.
  
          Check for a correctly populated template_hash and create if it doesn't
          already exist.