code: def ignore_unicode_prefix(f):
      
      if sys.version >= '3':
          # the representation of unicode string in Python 3 does not have prefix 'u',
          # so remove the prefix 'u' for doc tests
          literal_re = re.compile(r"(\W|^)[uU](['])", re.UNICODE)
          f.__doc__ = literal_re.sub(r'\1\2', f.__doc__)
      return f
docs: Ignore the 'u' prefix of string in doc tests, to make it works
      in both python 2 and 3