Better Regex and exception handling for this small code
On 2017-07-12 23:49, Nick Mellor wrote:
> On Wednesday, 12 July 2017 02:32:29 UTC+10, Ganesh Pal wrote:
>> 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
>> 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.strip()
>> checksumafter = crc.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
> There's not much need to compile regexes unless you've got *a lot* of them in your code. The first ones are automatically compiled and cached:
I think this is the first time that I've seen someone pass a compiled
pattern into re.findall.
The usual way is to pass the pattern as a string:
crc = re.findall(reg, logdata)
If you have a lot of them, or it's in a loop that'll iterate many times,
it'll be quicker if you compile it first (outside the loop):
pattern = re.compile(reg)
and then use the compiled pattern's .findall method:
crc = pattern.findall(logdata)