code: def safestr(str_):
      ''' get back an alphanumeric only version of source '''
      str_ = str_ or ""
      return "".join(x for x in str_ if x.isalnum()f safestr(str_):
      ''' get back an alphanumeric only version of source '''
      str_ = str_ or ""
      return "".join(x for x in str_ if x.isalnum())
docs: get back an alphanumeric only version of source