'Create, initialize, and send a new
:class:`~sleekxmpp.stanza.presence.Presence` stanza of
type ``\'subscribe\'``.
:param pto: The recipient of a directed presence.
:param pfrom: The sender of the presence.
:param ptype: The type of presence, such as ``\'subscribe\'``.
:param pnick: Optional nickname of the presence\'s sender.'

def send_presence_subscription(self, pto, pfrom=None, ptype=u'subscribe', pnick=None):

    self.make_presence(ptype=ptype, pfrom=pfrom, pto=JID(pto).bare, pnick=pnick).send()
