Python regex expression returns no match [duplicate]

Question

I am running Python 3.8.6 on Windows-10 machine.

I have been running a python script to parse log files with no issues until now, recently I migrated to rsyslog server running on Ubuntu.

The script fails on:

fields_data = re_data.match(line)

with error"

'NoneType' object has no attribute 'group'

Log string stored in variable 'line':

2020-12-18 13:34:37 - ive - [173.168.115.108] username(CCC Digital Certs)[All_Users] - Agent login succeeded for username/CCC Digital Certs from 173.168.115.108 with Pulse-Secure/9.0.3.1667 (Windows 10) Pulse/9.0.3.1667.#015

RegEx expression:

re_data = re.compile(r'(\d{4}.\d{2}.\d{2})\s(\d+.\d+.\d+)\s.+\[(\d+\.\d+\.\d+\.\d+)\]\s(\w+)')

I've tested the regex expression on line with the string shown below and it gives me the correct answer of 4 groups Date, Time, IP, Name.

Code:

fields_data = re_data.match(line)
out_file.write(f'{fields_data.group(1)},{fields_data.group(2)},{fields_data.group(3)},{fields_data.group(4)},login\n')

Patrick Artner · Accepted Answer · 2020-12-21 22:51:56Z

1

You are clearly not processing a line with a match. See re.match documentation

re.match(pattern, string, flags=0)
If zero or more characters at the beginning of string match the regular expression pattern, return a corresponding match object. Return None if the string does not match the pattern; note that this is different from a zero-length match. (emphasis mine)

Avoid this error by checking:

fields_data = re_data.match(line)
if fields_data and len(fields_data.groups()) > 4: # 0 + 4 groups == 5 minimum
    out_file.write(f'{fields_data.group(1)},{fields_data.group(2)},'
                   f'{fields_data.group(3)},{fields_data.group(4)},login\n')
else:
    print(f"Not a match: '{line}'")

or error handling (would suggest using checking here):

fields_data = re_data.match(line)
try:
    out_file.write(f'{fields_data.group(1)},{fields_data.group(2)},'
                   f'{fields_data.group(3)},{fields_data.group(4)},login\n')
except AttributeError: 
     pass

This kind of error often happens if you feed it "empty" lines in between or at the end of the file. Might want to check for that:

if not line.strip(): continue  # skip empty lines

edited Dec 21, 2020 at 22:51

answered Dec 21, 2020 at 22:46

Patrick Artner

51.9k10 gold badges50 silver badges79 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

salatwork Over a year ago

I read through the re.match documentation as suggested and I found th eproblem the new syslog server is adding a space at the front of the string, and you were correct the match fails. I corrected the error by putting the blank space in the search pattern. Now the script is running again. Thank You.

Collectives™ on Stack Overflow

Python regex expression returns no match [duplicate]

1 Answer 1

1 Comment

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Linked

Related