code: def _all_string_prefixes():
      # The valid string prefixes. Only contain the lower case versions,
      #  and don't contain any permutations (include 'fr', but not
      #  'rf'). The various permutations will be generated.
      _valid_string_prefixes = ["b", "r", "u", "f", "br", "fr"]
      # if we add binary f-strings, add: ['fb', 'fbr']
      result = {""}
      for prefix in _valid_string_prefixes:
          for t in _itertools.permutations(prefix):
              # create a list with upper and lower versions of each
              #  character
              for u in _itertools.product(*[(c, c.upper()) for c in t]):
                  result.add("".join(u))
      return result
  
imports: from builtins import open
  from codecs import lookup, BOM_UTF8
  import collections
  import functools
  from io import TextIOWrapper
  import itertools
  import re
  import sys
  from token import *
  from token import EXACT_TOKEN_TYPES
  import token
label_desc: Use image node_id 4 for calling a global function with example usage: _all_string_prefixes() and returns: result