def lookup_ip(self, mac):
		"""Look for a lease object with given mac address and return the
		assigned ip address.

		@type mac: str
		@rtype: str or None
		@raises ValueError:
		@raises OmapiError:
		@raises OmapiErrorNotFound: if no lease object with the given mac could be found
		@raises OmapiErrorAttributeNotFound: if lease could be found, but objects lacks a ip
		@raises socket.error:
		"""
		res = self.lookup_by_lease(mac=mac)
		try:
			return res["ip-address"]
		except KeyError:
			raise OmapiErrorAttributeNotFound()