proof of concept SRV resolver in ~35 LoC

srvres.py

from dns.resolver import Resolver
from itertools import groupby

from random import choices
choice = lambda *args,**kwargs: choices(*args,**kwargs)[0]

from operator import attrgetter
priority_sort = attrgetter("priority")

class SRVResolver:
	class Iterator:
		def __init__(self,grouped_records):
			self.records = grouped_records
		def __next__(self):
			if len(self.records)==0: raise StopIteration
			group = self.records[0]
			while len(group[1])==0:
				self.records.pop(0)
				if len(self.records)==0: raise StopIteration
				group = self.records[0]
			_, records = group # ditch priority value
			weights = [x.weight+1 for x in records]
			record = choice(records,weights)
			records.remove(record)
			return (record.target.to_text().rstrip("."),record.port)
	def __init__(self,service,domain,transport="tcp",resolver=None):
		if resolver is None: resolver=Resolver()
		self.qname = f"_{service}._{transport}.{domain}"
		self.resolver = resolver
	def __iter__(self):
		result = self.resolver.query(self.qname,"SRV")
		grouped_records = []
		for priority, records in groupby(sorted(result,key=priority_sort),priority_sort):
			grouped_records.append((priority,list(records)))
		return SRVResolver.Iterator(grouped_records)