def readlines_reverse(qfile):
    position = qfile.seek(-1, 1)
    line = b''
    while position >= 0:
        qfile.seek(position)
        next_char = qfile.read(1)
        if next_char == b"\n":
           yield line[::-1]
           line = b''
        else:
           line += next_char
        position -= 1
    yield line[::-1]

def logger_analyzer(fail_log, root_cause):
    with open('log.txt', 'rb') as f:
         num_fail_log = 0
         while not bytearray(fail_log, "utf8") in f.readline():
             num_fail_log += 1

         for num, line in enumerate(readlines_reverse(f)):
             if bytearray(root_cause, "utf8") in line:
                 break
    return num_fail_log - num + 1

logger_analyzer("FAIL", "testA")