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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sshclient_from_instance(instance, ssh_key_file, host_key_file='~/.ssh/known_hosts', user_name='root', ssh_pwd=None):
 """ Create and return an SSHClient object given an instance object. :type instance: :class`boto.ec2.instance.Instance` object :param instance: The instance object. :type ssh_key_file: str :param ssh_key_file: A path to the private key file used to log into instance. :type host_key_file: str :param host_key_file: A path to the known_hosts file used by the SSH client. Defaults to ~/.ssh/known_hosts :type user_name: str :param user_name: The username to use when logging into the instance. Defaults to root. :type ssh_pwd: str :param ssh_pwd: The passphrase, if any, associated with private key. """

    s = FakeServer(instance, ssh_key_file)
    return SSHClient(s, host_key_file, user_name, ssh_pwd)