code: def identifier(self):
          
          identifier = self._hs._local_identifiers.get(
              self.__class__.__name__, self._hs._local_identifiers.get(
                  'Create', self._identifier))
          if not self._rx_identifier.match(identifier):
              raise ValueError(
                  "identifier '%s' does not match pattern '%s'"
                  % (identifier, self._rx_identifier.pattern))
          return identifier
docs: The identifier (symbol) that is used when printing the annihilation
          operator. This is identical to the identifier of :class:`Create`. A
          custom identifier for both :class:`Destroy` and :class:`Create` can be
          set through the `local_identifiers` parameter of the associated Hilbert
          space::
  
              >>> hs_custom = LocalSpace(0, local_identifiers={'Destroy': 'b'})
              >>> Create(hs=hs_custom).identifier
              'b'
              >>> Destroy(hs=hs_custom).identifier
              'b'