def load_host_keys(filename):
from paramiko.hostkeys import HostKeys<EOL>return HostKeys(filename)<EOL>
Read a file of known SSH host keys, in the format used by openssh, and
return a compound dict of ``hostname -> keytype ->`` `PKey
<paramiko.pkey.PKey>`. The hostname may be an IP address or DNS name.  The
keytype will be either ``"ssh-rsa"`` or ``"ssh-dss"``.

This type of file unfortunately doesn't exist on Windows, but on posix,
it will usually be stored in ``os.path.expanduser("~/.ssh/known_hosts")``.

Since 1.5.3, this is just a wrapper around `.HostKeys`.

:param str filename: name of the file to read host keys from
:return:
    nested dict of `.PKey` objects, indexed by hostname and then keytype