code: def sanitize(self, s):
          
          if not isinstance(s, six.string_types):
              return s
  
          """
          re.sub matches a regex and replaces it with another.
          The regex replacements are taken from a file if the option
          is passed when py.test is called. Otherwise, the strings
          are not processed
          """
          for regex, replace in six.iteritems(self.parent.sanitize_patterns):
              s = re.sub(regex, replace, s)
          return s
docs: sanitize a string for comparison.