<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def unpack_mac(sixbytes):
 	"""Converts a mac address given in a six byte string in network 	byte order to a string in colon delimited notation. 	'30:31:32:33:34:35' 	Traceback (most recent call last):
 	ValueError: given buffer is not exactly six bytes long 	@type sixbytes: bytes 	@rtype: str 	@raises ValueError: for bad input 	"""

	if not isinstance(sixbytes, bytes):
		raise ValueError("given buffer is not a string")
	if len(sixbytes) != 6:
		raise ValueError("given buffer is not exactly six bytes long")
	return ":".join(["%2.2x".__mod__(x) for x in bytes_to_int_seq(sixbytes)])