Description of problem:

It looks like there is some conflicting docs in pythons domain lookup documentation: 

http://libvirt.org/docs/libvirt-appdev-guide-python/en-US/html/libvirt_application_development_guide_using_python-Guest_Domains.html

vs

https://libvirt.org/python.html



Specifically, this part:

dom = conn.lookupByName(domainName)
if dom == None:
    print('Failed to get the domain object', file=sys.stderr)

vs

try:
    dom0 = conn.lookupByName("Domain-0")
except:
    print 'Failed to find the main domain'


On the version of python-libvirt that I'm using (1.2.2 on ubuntu 14.04) when conn.lookupByName cannot find the domain name, it raises a libvirt.libvirtError, with err.get_error_code() == libvirt.VIR_ERR_NO_DOMAIN. This is also the case for lookupById() and lookupByUuid(). Assuming this wasn't behavior that was recently changed, the appdev docs should be updated to reflect this.