IPv4 address substitution in Python script

Question

I'm having trouble getting this to work, and I am hoping for any ideas:

My goal: to take a file, read it line by line, substitute any IP address for a specific substitute, and write the changes to the same file.

I KNOW THIS IS NOT CORRECT SYNTAX

Pseudo-Example:

$ cat foo
10.153.193.0/24 via 10.153.213.1

def swap_ip_inline(line):
  m = re.search('some-regex', line)
  if m:
    for each_ip_it_matched:
      ip2db(original_ip)
    new_line = reconstruct_line_with_new_ip()

    line = new_line

  return line

for l in foo.readlines():
  swap_ip_inline(l)

do some foo to rebuild the file.

I want to take the file 'foo', find each IP in a given line, substitute the ip using the ip2db function, and then output the altered line.

Workflow: 1. Open File 2. Read Lines 3. Swap IP's 4. Save lines (altered/unaltered) into tmp file 5. Overwrite original file with tmp file

*edited to add pseudo-code example

I'm not sure how you expect us to help you ? You didn't provide any code. — HamZa, Nov 26 '13 at 18:53
See: [Regular expression to match hostname or IP Address?](http://stackoverflow.com/q/106179/1497596) — DavidRR, Nov 26 '13 at 20:07

score 2 · Answer 1 · answered Nov 26 '13 at 20:41

2

Here you go:

>>> import re
>>> ip_addr_regex = re.compile(r'\b(?:[0-9]{1,3}\.){3}[0-9]{1,3}\b')
>>> f = open('foo')
>>> for line in f:
...     print(line)
...
10.153.193.0/24 via 10.153.213.1

>>> f.seek(0)
>>>

specific_substitute = 'foo'

>>> for line in f:
...     re.sub(ip_addr_regex, specific_substitute, line)
...
'foo/24 via foo\n'

answered Nov 26 '13 at 20:41

cog_n1t1v3

229
4
18

ssheth, That's similar to what I had. The problem I have is that I need to run a match before the sub so I can evaluate the IP addresses in a given line. I want to have a 1:1 replacement for each occurrence of a given IP address, and I can't quite figure out how to go about it. I've tried what's above, and I've tried splitting each line using .split() and re.search.groups(), and I can't refine the regex enough to give me JUST the IP address if there aren't spaces, etc. around it. If I could call a group into the substitute function for re.sub that would be it. Does that make sense? – jduncan Nov 27 '13 at 02:27

score 0 · Accepted Answer · edited May 23 '17 at 12:12

This link gave me the breatkthrough I was looking for:

Python - parse IPv4 addresses from string (even when censored)

a simple modification passes initial smoke tests:

def _sub_ip(self, line):
    pattern = r"((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)([ (\[]?(\.|dot)[ )\]]?(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3})"
    ips = [each[0] for each in re.findall(pattern, line)]
    for item in ips:
        location = ips.index(item)
        ip = re.sub("[ ()\[\]]", "", item)
        ip = re.sub("dot", ".", ip)
        ips.remove(item)
        ips.insert(location, ip)

    for ip in ips:
        line = line.replace(ip, self._ip2db(ip))

    return line

I'm sure I'll clean it up down the road, but it's a great start.

IPv4 address substitution in Python script

2 Answers2