Determine Whether File Exists On HTTP Server

[OvErboRed]

Hi, I'm trying to determine whether a given URL exists. I'm new to Python 
but I think that urllib is the tool for the job. However, if I give it a 
non-existent file, it simply returns the 404 page. Aside from grepping this 
for '404', is there a better way to do this? (Preferrably, there is a 
solution that can be applied to both HTTP and FTP.) Thanks in advance.