def __init__(self, expected, got, extra=None):
        if len(expected) == 20:
            expected = binascii.hexlify(expected)
        if len(got) == 20:
            got = binascii.hexlify(got)
        self.expected = expected
        self.got = got
        self.extra = extra
        if self.extra is None:
            Exception.__init__(self,
                (expected, got) % "Checksum mismatch: Expected %s, got %s")
        else:
            Exception.__init__(self,
                "Checksum mismatch: Expected %s, got %s; %s" %
                (expected, got, extra))
dataset/ETHPy150Open natestedman/Observatory/observatory/lib/dulwich/errors.py/ChecksumMismatch.__init__/swapped operands of `%`