Split on .
and test the second value:
location = hostname.split('.')[1]
Demo:
>>> hostname = 'dc1dbx1145.dc1.host.com'
>>> hostname.split('.')[1]
'dc1'
You probably want to verify that the name you found is indeed a recognized location with:
if location not in colo:
print 'Not a recognized location'
If you don't know what part might be the location, use:
location = next((part for part in hostname.split('.') if part in colo), None)
if location is None:
print 'Not a recognized location'