Hypervisor connection是libvirt一个核心概念（以下内容摘自这里）：
A connection is the primary or top level object in the libvirt API and Python libvirt module. An instance of this object is required before attempting to use almost any of the classes or methods. A connection is associated with a particular hypervisor, which may be running locally on the same machine as the libvirt client application, or on a remote machine over the network. In all cases, the connection is represented by an instance of the virConnect class and identified by a URI. The URI scheme and path defines the hypervisor to connect to, while the host part of the URI determines where it is located.
An application is permitted to open multiple connections at the same time, even when using more than one type of hypervisor on a single machine. For example, a host may provide both KVM full machine virtualization and LXC container virtualization. A connection object may be used concurrently across multiple threads. Once a connection has been established, it is possible to obtain handles to other managed objects or create new managed objects.
以下代码测试Xen连接：
#!/usr/bin/python
from __future__ import print_function
import sys
import libvirt
conn = libvirt.open('xen:///')
if conn == None:
print('Failed to open connection to xen:///', file=sys.stderr)
exit(1)
else:
print('Open connection success', file=sys.stdout)
conn.close()
exit(0)