Python Regular Expression to find exception in log file - python-3.x

Question

I am writing a script to parse the logs. I need a regular expression to find the python exception in the log file, if any.
For example if below exception is in the log file, it should return below exception in string format.
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<string>", line 1, in <module>
NameError: name 'klj' is not defined
I tried below code, it won't work:
import urllib.request
import re
txt = urllib.request.urlopen(log_url).read().decode('utf-8')
exceptions = re.findall("(\w+)Error:", txt)
Thanks in Advance

Answer 1

Your regex was only looking for exception names that ended in 'Error', but many end in 'Exception'. And you were capturing in capture group 1 only the characters that preceded 'Error', so you would not get the full name.
The following regex will look only for exception names at the start of a line and capture the full name:
import re
txt = """Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<string>", line 1, in <module>
NameError: name 'klj' is not defined"""
exceptions = re.findall("""(?x) # Verbose mode
(?m) # Multiline mode (^ matches start of a line)
^ # Match start of a line
(?:\w+) # Match one or more word characters in a non-capturing group
(?:Error|Exception) # Match 'Error' or 'Exception':
(?=: ) # Lookahead assertion: next characters are ': '
""", txt)
print(exceptions)
Prints:
['NameError']