text: """Internet Group Management Protocol."""
  
  from pypacker import pypacker, checksum
  from pypacker.pypacker import FIELD_FLAG_AUTOUPDATE
  
  
  class IGMP(pypacker.Packet):
  	__hdr__ = (
  		("type", "B", 0),
  		("maxresp", "B", 0),
  		("sum", "H", 0, FIELD_FLAG_AUTOUPDATE),
  		("group", "4s", b"\x00" * 4)
  	)
  
  	# Convenient access for: group[_s]
  	group_s = pypacker.get_property_ip4("group")
  
  	def _update_fields(self):
  		if self.sum_au_active and self._changed():
  			self.sum = 0
  			self.sum = checksum.in_cksum(pypacker.Packet.bin(self))
  