Can this be reduced to one regex

Question

Would it be possible to reduce these patterns into one pattern ?

PRIV_LOC = re.compile("^127\.\d{1,3}\.\d{1,3}\.\d{1,3}$")
PRIV_24 = re.compile("^10\.\d{1,3}\.\d{1,3}\.\d{1,3}$")
PRIV_20 = re.compile("^192\.168\.\d{1,3}.\d{1,3}$")
PRIV_16 = re.compile("^172.(1[6-9]|2[0-9]|3[0-1]).[0-9]{1,3}.[0-9]{1,3}$")


def is_ip_private(ip):
    return PRIV_LOC.match(ip) or PRIV_24.match(ip) or PRIV_20.match(ip) or PRIV_16.match(ip)

You clearly know how to do OR in a regex, so of course it can be combined. But the impact on readability would probably be unhelpful. — jonrsharpe, Jul 21 '17 at 19:55
[How do you determine if an IP address is private, in Python?](https://stackoverflow.com/q/691045/1324033) — Sayse, Jul 21 '17 at 20:01
`.\d{1,3}` isn't valid for ip address this would accept (.999 and .256 both of which aren't allowed — depperm, Jul 21 '17 at 20:12

score 1 · Accepted Answer · answered Jul 21 '17 at 20:03

You can try this:

re.compile(r"^(127\.\d{1,3}\.\d{1,3}\.\d{1,3}|10\.\d{1,3}\.\d{1,3}\.\d{1,3}|192\.168\.\d{1,3}.\d{1,3}|172.(1[6-9]|2[0-9]|3[0-1]).[0-9]{1,3}.[0-9]{1,3})$")

Or this, to not lose readability much:

re.compile(r"^(" + '|'.join([
    r"127\.\d{1,3}\.\d{1,3}\.\d{1,3}", # PRIV_LOC
    r"10\.\d{1,3}\.\d{1,3}\.\d{1,3}", # PRIV_24
    r"192\.168\.\d{1,3}.\d{1,3}", # PRIV_20
    r"172.(1[6-9]|2[0-9]|3[0-1]).[0-9]{1,3}.[0-9]{1,3}" # PRIV_16
]) + r")$")

Can this be reduced to one regex

1 Answers1