code: def _in(field, value, document):
      
      try:
          values = iter(value)
      except TypeError:
          raise MalformedQueryException("'$in' must accept an iterable")
  
      return document.get(field, None) in values
docs: Returns True if document[field] is in the interable value. If the
      supplied value is not an iterable, then a MalformedQueryException is raised