Because on Py3:

        def test_dumpreader():
            in_ = b"""\
        txn 0123456789abcdef " "
        user "my name"
        description "o la-la..."
        extension "zzz123 def"
        obj 0000000000000001 delete
        obj 0000000000000002 from 0123456789abcdee
        obj 0000000000000003 54 adler32:01234567 -
        obj 0000000000000004 4 sha1:9865d483bc5a94f2e30056fc256ed3066af54d04
        ZZZZ
        obj 0000000000000005 9 crc32:52fdeac5
        ABC

        DEF!

        txn 0123456789abcdf0 " "
        user "author2"
        description "zzz"
        extension "qqq"

        """

            r = DumpReader(BytesIO(in_))
            t1 = r.readtxn()
            assert isinstance(t1, Transaction)
    >       assert t1.tid == '0123456789abcdef'.decode('hex')
    E       AttributeError: 'str' object has no attribute 'decode'

    test/test_dump.py:77: AttributeError

Based on patch by Jérome Perrin.