regular expressions: why '$' is not working with '\n'

Asked May 08 '18 at 11:21

Active May 08 '18 at 11:36

Viewed 45 times

import re
def ipv4_address(address):
    match = re.search(r"^((2[0-5][0-5]|1[0-9][0-9]|[1-9][0-9]|[0-9])\.){3}(2[0-5][0-5]|1[0-9][0-9]|[1-9][0-9]|[0-9])$", address)   
    if match: return True
    else: return False

print(ipv4_address("127.0.0.1\n"))

I don`t understand why '$' is not working with '\n'

simpler test:

>>> bool(re.match("^ABC$","ABC\n"))
True

edited May 08 '18 at 11:36

Jean-François Fabre

137,073
23
153
219

asked May 08 '18 at 11:21

Artur Gaio Pinto

Use the `ipaddress` module. – heemayl May 08 '18 at 11:24
interesting point though: how `\n` is ignored. must be another solved issue here. If I don't find a suitable duplicate I'll reopen – Jean-François Fabre May 08 '18 at 11:29
1

This regex doesn't accept `249.249.249.249`. I believe there is a problem with the logic as well. You can check out https://stackoverflow.com/questions/3462784/check-if-a-string-matches-an-ip-address-pattern-in-python – Bora May 08 '18 at 11:30
ok, thanks! @Jean-FrançoisFabre – Artur Gaio Pinto May 08 '18 at 11:31
@Bora it does accept 249.249.249.249 – Artur Gaio Pinto May 08 '18 at 11:32
I think you should use the duplicate links to validate ip addresses, BUT I admit I'm puzzled by the \n thing. – Jean-François Fabre May 08 '18 at 11:33
for example your question would have been better if just asking why `re.match("^ABC$","ABC\n")` returns a match. no need to mix ip addresses in the question – Jean-François Fabre May 08 '18 at 11:33
It's a re.search, not a re.match, and the pattern isn't multiline. `\n` separates lines, so $ matches the end of line before it. Edit: Still confused, docs seem to indicate this should only happen if it *is* multiline. – Yann Vernier May 08 '18 at 11:34
@YannVernier ok try with `match` (I have added a simpler example, the IP think was misleading) – Jean-François Fabre May 08 '18 at 11:37
Replace `$` with `\Z` as `$` matches a location before a final newline in the input string. – Wiktor Stribiżew May 08 '18 at 11:38
@WiktorStribiżew it worked! thanks! but why does '$' matches before a final newline? Isn`t it supposed to stop everything afterwards? – Artur Gaio Pinto May 08 '18 at 11:41
1

[`re` docs say](https://docs.python.org/2/library/re.html): *`'$'` Matches the end of the string **or just before the newline at the end of the string*** – Wiktor Stribiżew May 08 '18 at 11:43
is there a duplicate of this somewhere? – Jean-François Fabre May 08 '18 at 11:47

regular expressions: why '$' is not working with '\n'

0 Answers0