code: def _validate_excludes(self, excludes, field, value):
          
          if isinstance(excludes, Hashable):
              excludes = [excludes]
  
          # Save required field to be checked latter
          if 'required' in self.schema[field] and self.schema[field]['required']:
              self._unrequired_by_excludes.add(field)
          for exclude in excludes:
              if (exclude in self.schema and
                  'required' in self.schema[exclude] and
                      self.schema[exclude]['required']):
  
                  self._unrequired_by_excludes.add(exclude)
  
          if [True for key in excludes if key in self.document]:
              # Wrap each field in `excludes` list between quotes
              exclusion_str = ', '.join("'{0}'"
                                        .format(word) for word in excludes)
              self._error(field, errors.EXCLUDES_FIELD, exclusion_str)
docs: {'type': ('hashable', 'list'),
               'schema': {'type': 'hashable'}}