requires python 3.5+ and dnslib, see https://github.com/samuelcolvin/dnserver for full/better implementation

dns_server.py

from datetime import datetime
from time import sleep

from dnslib import DNSLabel, QTYPE, RD, RR
from dnslib import A, AAAA, CNAME, MX, NS, SOA, TXT
from dnslib.server import DNSServer

EPOCH = datetime(1970, 1, 1)
SERIAL = int((datetime.utcnow() - EPOCH).total_seconds())

TYPE_LOOKUP = {
    A: QTYPE.A,
    AAAA: QTYPE.AAAA,
    CNAME: QTYPE.CNAME,
    MX: QTYPE.MX,
    NS: QTYPE.NS,
    SOA: QTYPE.SOA,
    TXT: QTYPE.TXT,
}


class Record:
    def __init__(self, rdata_type, *args, rtype=None, rname=None, ttl=None, **kwargs):
        if isinstance(rdata_type, RD):
            # actually an instance, not a type
            self._rtype = TYPE_LOOKUP[rdata_type.__class__]
            rdata = rdata_type
        else:
            self._rtype = TYPE_LOOKUP[rdata_type]
            if rdata_type == SOA and len(args) == 2:
                # add sensible times to SOA
                args += ((
                    SERIAL,  # serial number
                    60 * 60 * 1,  # refresh
                    60 * 60 * 3,  # retry
                    60 * 60 * 24,  # expire
                    60 * 60 * 1,  # minimum
                ),)
            rdata = rdata_type(*args)

        if rtype:
            self._rtype = rtype
        self._rname = rname
        self.kwargs = dict(
            rdata=rdata,
            ttl=self.sensible_ttl() if ttl is None else ttl,
            **kwargs,
        )

    def try_rr(self, q):
        if q.qtype == QTYPE.ANY or q.qtype == self._rtype:
            return self.as_rr(q.qname)

    def as_rr(self, alt_rname):
        return RR(rname=self._rname or alt_rname, rtype=self._rtype, **self.kwargs)

    def sensible_ttl(self):
        if self._rtype in (QTYPE.NS, QTYPE.SOA):
            return 60 * 60 * 24
        else:
            return 300

    @property
    def is_soa(self):
        return self._rtype == QTYPE.SOA

    def __str__(self):
        return '{} {}'.format(QTYPE[self._rtype], self.kwargs)


ZONES = {
    'example.com': [
        Record(A, '1.2.3.4'),
        Record(CNAME, 'whever.com'),
        Record(MX, 'whatever.com.', 5),
        Record(MX, 'mx2.whatever.com.', 10),
        Record(MX, 'mx3.whatever.com.', 20),
        Record(NS, 'mx2.whatever.com.'),
        Record(NS, 'mx3.whatever.com.'),
        Record(TXT, 'hello this is some text'),
        Record(SOA, 'ns1.example.com', 'dns.example.com'),
    ]
}


class Resolver:
    def __init__(self):
        self.zones = {DNSLabel(k): v for k, v in ZONES.items()}

    def resolve(self, request, handler):
        reply = request.reply()
        zone = self.zones.get(request.q.qname)
        if zone is not None:
            for zone_records in zone:
                rr = zone_records.try_rr(request.q)
                rr and reply.add_answer(rr)
        else:
            # no direct zone so look for an SOA record for a higher level zone
            for zone_label, zone_records in self.zones.items():
                if request.q.qname.matchSuffix(zone_label):
                    try:
                        soa_record = next(r for r in zone_records if r.is_soa)
                    except StopIteration:
                        continue
                    else:
                        reply.add_answer(soa_record.as_rr(zone_label))
                        break

        return reply


resolver = Resolver()
servers = [
    DNSServer(resolver, port=5053, address='localhost', tcp=True),
    DNSServer(resolver, port=5053, address='localhost', tcp=False),
]

if __name__ == '__main__':
    for s in servers:
        s.start_thread()

    try:
        while 1:
            sleep(0.1)
    except KeyboardInterrupt:
        pass
    finally:
        for s in servers:
            s.stop()

nicely done.

for whoever interested, if you want the server to return the same records as example.com for non-existent zones change line 92 to:
zone = self.zones.get(request.q.qname,self.zones[DNSLabel('example.com')])

then the server will always return an answer.