code: def parse_single(str_):
      
      if str_ is None:
          return ''
  
      str_ = str_.strip()
  
      if not str_:
          return ''
  
      if BOOL_PATTERN.match(str_) is not None:
          return bool(str_)
  
      if INT_PATTERN.match(str_) is not None:
          return int(str_)
  
      if STR_PATTERN.match(str_) is not None:
          return str_[1:-1]
  
      return str_
docs: Very simple parser to parse expressions represent some single values.
  
      :param str_: a string to parse
      :return: Int | Bool | String
  
      >>> parse_single(None)
      ''
      >>> parse_single("0")
      0
      >>> parse_single("123")
      123
      >>> parse_single("True")
      True
      >>> parse_single("a string")
      'a string'
      >>> parse_single('"a string"')
      'a string'
      >>> parse_single("'a string'")
      'a string'
      >>> parse_single("0.1")
      '0.1'
      >>> parse_single("    a string contains extra whitespaces     ")
      'a string contains extra whitespaces'