simple port scanner

Strange, but well-known scanning tool nmap has a quite aggressive license. It is in fact GNU GPL Version 2 but with some exceptions. Among others there is one which may force you not to use nmap in your scripts:

 * Note that the GPL places important restrictions on "derived works", yet *
 * it does not provide a detailed definition of that term.  To avoid       *
 * misunderstandings, we consider an application to constitute a           *
 * "derivative work" for the purpose of this license if it does any of the *
 * following:                                                              *
...
 * o Executes Nmap and parses the results (as opposed to typical shell or  *
 *   execution-menu apps, which simply display raw Nmap output and so are  *
 *   not derivative works.)                                                * 

This is very confusing and I've decided to write my own port scanner for uguu which is BSD-licensed. Needless to say, we planned to use nmap originally. With having our own tool we strike several goals at once: no nmap license terms violation, no external program execution in our python scripts, lessen the number external parts uguu is depended on, scan a list of host-port pairs at once without grouping by ports (you can give nmap list of hosts through stdin but you can't specify ports there, afaik). And with all these advantages it was fine by me to have a scanner with less performance. But as for my small /24 network with 4 computers and no crappy firewalls it is even faster than nmap (nmap -PS -p): 3 seconds against 8 seconds.

The scanner is written in python and is available as a part of uguu codebase (bin/network.py). It can be executed as a standalone application with ip range (three formats are available: single host, ip1-ip2, ip/netmask) and port specified in command line. Ip range can't be large for now due to number of open files limitations, but it worked for me with /24 netmask.

PS. Should I pass some other options to nmap? But no cheating here, it has to be a user-invoked port scanner.