Python exercise - alternative solution

I promised to post an alternative solution to a Python exercise for an on-site today. For other interested parties, the code lists unused ports from /etc/services:

import sys

# set the file name depending on the operating system
if sys.platform == 'win32':
    file = r'C:\WINDOWS\system32\drivers\etc\services'
else:
    file = '/etc/services'

# Create an empty dictionary
ports = dict()

# Iterate through the file, one line at a time
for line in open(file):

   # Ignore lines starting with '#' and those containing only whitespace
   if line[0:1] != '#' and not line.isspace():

       # Extract the second field (seperated by \s+)
       pp = line.split(None, 1)[1]

       # Extract the port number from port/protocol
       port = pp.split ('/', 1)[0]

       # Convert to int, then store as a dictionary key
       port = int(port)
       ports[port] = None
   
       # Give up after port 200
       if port > 200: break

# Print any port numbers not present as a dictionary key
for num in xrange(1,201):
    if not num in ports:
        print "Unused port", num

Here is a smaller solution using Regular Expressions:

import sys,re

file = r'C:\WINDOWS\system32\drivers\etc\services' \
    if sys.platform == 'win32' else '/etc/services'

found = set()
for line in open(file):       
    m = re.search(r'^[^#].*\s(\d+)/(tcpudp)\s',line)
    if m:
       port = int(m.groups()[0])
       if port > 200: break
       found.add(port)
     
print set(range(1,201)) - found