Better Regex and exception handling for this small code

[Ganesh Pal]

Dear Python friends

I am trying to open a file and check if there is a pattern  has  changed
after the task got completed?

file data:
........................................................

#tail -f /file.txt
..........................................
Note: CRC:algo = 2, split_crc = 1, unused = 0, initiator_crc = b6b20a65,
journal_crc = d2097b00
Note: Task completed successfully.
Note: CRC:algo = 2, split_crc = 1, unused = 0, initiator_crc = d976d35e,
journal_crc = a176af10


 I  have the below piece of code  but would like to make this better more
pythonic , I found regex pattern and exception handling poor here , any
quick suggestion in your spare time is welcome.


#open the existing file if the flag is set and check if there is a match

log_file='/file.txt'
flag_is_on=1

data = None
with open(log_file, 'r') as f:
     data = f.readlines()


if flag_is_on:
    logdata = '\n'.join(data)
    reg = "initiator_crc =(?P<ini_crc>[\s\S]*?), journal_crc"
    crc = re.findall(re.compile(reg), logdata)
    if not crc:
        raise Exception("Pattern not found in  logfile")

    checksumbefore = crc[0].strip()
    checksumafter = crc[1].strip()
    logging.info("checksumbefore :%s and  checksumafter:%s"
                      % (checksumbefore, checksumafter))

    if checksumbefore == checksumafter:
       raise Exception("checksum not macthing")

I am  on Linux and Python 2.7

Regards,
Ganesh