class_docstr: Subclass of argparse.Action to avoid multiple of the same choice from a list
class_docstr_tok: ["Subclass","of","argparse.Action","to","avoid","multiple","of","the","same","choice","from","a","list"]
code: def __call__(self, parser, namespace, values, option_string=None):
      unique_items = set(values)
      setattr(namespace, self.dest, sorted(unique_items))
  
imports: from abc import abstractmethod
  from argparse import _AppendAction, Action, ArgumentTypeError, RawDescriptionHelpFormatter
  import os
  import textwrap
  from streamalert.apps.config import AWS_RATE_RE, AWS_RATE_HELPER
label_desc: Use image node_id 1 for calling the UniqueSortedListAction obj's underlying member method code with example usage: obj.__call__(parser, namespace, values, option_string) without return types