error return from urlopen

When I direct urlopen to a non-existent server process I get

IOError: [Errno socket error] (10061, 'Connection refused')
The connection refused is as expected but whats the 10061?
strerror(10061) says 'unknown error'

So its like an errno but not quite an errno?
Can I find out more about this number like I can about errno?

Rustom Mody