@pipe.func<EOL>def format(prev, format_string):
for i in prev:<EOL><INDENT>yield (format_string % i)<EOL><DEDENT>
The pipe formats the data passed from previous generator according to
    given format_string argument.

    :param prev: The previous iterator of pipe.
    :type prev: Pipe
    :param format_string: format string which used to format the data from
                          previous iterator.
    :type sequence: str
    :returns: generator