code: def pattern(self):
          
          value = self._schema.get("pattern", None)
          if value is None:
              return
          try:
              return re.compile(value)
          except re.error as ex:
              raise SchemaError(
                  "pattern value {0!r} is not a valid regular expression:"
                  " {1}".format(value, str(ex)))
docs: Regular expression describing valid objects.
  
          .. note::
              JSON schema specifications says that this value SHOULD
              follow the ``EMCA 262/Perl 5`` format. We cannot support
              this so we support python regular expressions instead. This
              is still valid but should be noted for clarity.
  
          :returns:
              None or compiled regular expression