Python Regex Match sub-string

Question

I have the following string:

spf=pass (sender IP is 198.71.245.6) smtp.mailfrom=bounces.em.godaddy.com; domainname.com.au; dkim=pass (signature was verified) header.d=godaddy.com;domainname.com.au; dmarc=pass action=none header.from=godaddy.com;

With the following code:

if "Authentication-Results" in n:
    auth_results = n['Authentication-Results']
    print(auth_results)

    spf = re.match(r"spf=(\w+)", auth_results)
    if spf:
       spf_result = spf.group(1)

    dkim = re.match(r"^.*dkim=(\w+)", auth_results)
    print(dkim)
    if dkim:
        dkim_result = dkim.group(1)

The SPF always matches but the DKIM doesn't:

print(dkim) = None

According to the regex testers online it should: https://regex101.com/r/ZkVg74/1 any ideas why it's not i also tried these:

dkim = re.match(r"dkim=(\w+)", auth_results) dkim = re.match(r"^.*dkim=(\w+)", auth_results, re.MULTILINE)

is that string at the top all one string or a few different ones? — Henry
– Henry, Commented Oct 8, 2018 at 2:30

blhsing · Accepted Answer · 2018-10-08 02:42:20Z

1

. does not match a newline character by default. Since the dkim in your test string is on the second line and your regex pattern tries to match any non-newline character from the beginning of the string with ^.*, it would not find dkim on the second line. You should either use the re.DOTALL flag to allow . to match a newline character:

dkim = re.match(r"^.*dkim=(\w+)", auth_results, flags=re.DOTALL)

or remove the unnecessary match from the beginning of the string altogether:

dkim = re.search(r"dkim=(\w+)", auth_results)

answered Oct 8, 2018 at 2:42

blhsing

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1 Comment

Lee Stevens Over a year ago

Thank you, adding the re.DOTALL fixed my issue.

lincr · Accepted Answer · 2018-10-08 02:41:32Z

0

First, re.match works from the beginning. so your r"dkim=(\w+)" trial doesn't work.

Second, the . symbol matches characters except the new line character. If you want it to, you should explictly force it using re.S or re.DOTALL flag.

Also, you can use [\s\S] or [\w\W] to match any characters.

Try this:
re.match(r"^[\s\S]*dkim=(\w+)", auth_results).group(1)
or this:
re.match(r"^.*dkim=(\w+)", auth_results, re.DOTALL).group(1)

answered Oct 8, 2018 at 2:41

lincr

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