在awsfabric中将实例添加到env

Question

从这个Python结构程序中，我应该打印EC2实例的细节。

@task
def ec2_print_instance(full=False):
    """
    Print EC2 instance info.

    :param full: Print all attributes, or just the most useful ones? Defaults
        to ``False``.
    """
    instancewrapper = Ec2InstanceWrapper.get_from_host_string()
    print 'Instance:', instancewrapper['id']
    print_ec2_instance(instancewrapper.instance, full=full)

上面的方法调用以下类EC2InstanceWrapper。

class Ec2InstanceWrapper(object): 
    def __init__(self, instance):
       self.instance = instance
    def __getitem__(self, key):
       return getattr(self.instance, key)
    def __str__(self):
       return 'Ec2InstanceWrapper:{0}'.format(self)
    def add_instance_to_env(self):
       if not 'ec2instances' in env:
            env['ec2instances'] = {}
        env['ec2instances'][self.get_ssh_uri()] = self
        if not env.key_filename:
            env.key_filename = []
        key_filename = self.get_ssh_key_filename()
        if not key_filename in env.key_filename:
            env.key_filename.append(key_filename)
    @classmethod
    def get_from_host_string(cls):
        """
        If an instance has been registered in ``fabric.api.env`` using
        :meth:`add_instance_to_env`, this method can be used to get
        the instance identified by ``fabric.api.env.host_string``.
        """
        return env.ec2instances[env.host_string]

如果我运行此程序，则获取AttributeError：ec2instances。 我需要使用add_instance_to_env方法将我的主机添加到env。怎么做？