Doh! I misread "a" as host instead of ip in your first post. I'm sorry about that; I really must slow down. Anyhow,
I believe you can still do this with only compiling a regex once and then performing a few substitutions on the hostname. Substitutions: 1st byte of IP => (0) 2nd byte of IP => (1) 3rd byte of IP => (2) 4th byte of IP => (3) and likewise for hex => (x0) (x1) (x2) (x3) Each host string will possibly map into multiple expansions, esp. if a number repeats itself in the IP, or if an IP byte is less than 10 (such that the decimal and hex representations are the same). Zero-padded and unpadded will both have to be substituted, and it's probably best to not to alter the last two fields in the host name since ISPs can't change those. With this scheme, here are a few expansions of (ip,host) tuples: 172.182.240.186 ACB6F0BA.ipt.aol.com becomes (x0)(x1)(x2)(x3).ipt.aol.com 67.119.55.77 adsl-67-119-55-77.dsl.lsan03.pacbell.net becomes adsl-(0)-(1)-(2)-(3).dsl.lsan03.pacbell.net adsl-(0)-(1)-(2)-(x1).dsl.lsan03.pacbell.net 81.220.220.143 ip-143.net-81-220-220.henin.rev.numericable.fr becomes ip-(3).net-(0)-(1)-(1).henin.rev.numericable.fr ip-(3).net-(0)-(1)-(2).henin.rev.numericable.fr ip-(3).net-(0)-(2)-(1).henin.rev.numericable.fr ip-(3).net-(0)-(2)-(2).henin.rev.numericable.fr etcetera. Now you can run a precompiled regular expression against these hostname permutations, i.e. ".*\(0\).*\(1\).*\(2\).*\(3\).*" would match any host in which the IP address numbers appeared in the correct order. There are only a handful dynamic addresses in your sample data that don't match a decimal or hexadecimal IP-based pattern, e.g. 68.53.109.99 pcp03902856pcs.nash01.tn.comcast.net 68.147.136.167 s01060050bf91c1e4.cg.shawcable.net -- http://mail.python.org/mailman/listinfo/python-list
