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()

In all fairness, to whomever ends up here. Record(A, '1.2.3.4') defaults to all responses because it appends the domain from the request. Now, this becomes a slight issue of readability and user friendliness when you try to do Record(A, 'www.example.com', '1.2.3.4'). If you assume this, this code will break. I'm pretty sure that's confusing unless you know what's going on in dnslib or how to adapt this code.

Also doing rr and reply.add_answer(rr) is an odd reading, especially if you're used to actually using if blocks the way they were meant to be used. Just as I'm sure someone who's been in the game long enough and comes from another language background will figure that out pretty quick. But there are some things here that makes this code work, but not necessarily easy to understand or adapt.

Anyone ending up here, actually use the sticky link at the top.

could you please help me with SRV record.

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.