两个Fundations of python network programming 上的例子

首先安装dnspython3

pip3 install dnspython3

import argparse, dns.resolver

def lookup(name):
    for qtype in 'A', 'AAAA', 'CNAME', 'MX', 'NS':
        answer = dns.resolver.query(name, qtype, raise_on_no_answer=False)
        if answer.rrset is not None:
            print(answer.rrset)

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Resolve a name using DNS')
    parser.add_argument('name', help='name that you want to look up in DNS')
    lookup(parser.parse_args().name)

import argparse, dns.resolver

def resolve_hostname(hostname, indent=''):
    "Print an A or AAAA record for `hostname`; follow CNAMEs if necessary."
    indent = indent + '    '
    answer = dns.resolver.query(hostname, 'A')
    if answer.rrset is not None:
        for record in answer:
            print(indent, hostname, 'has A address', record.address)
        return
    answer = dns.resolver.query(hostname, 'AAAA')
    if answer.rrset is not None:
        for record in answer:
            print(indent, hostname, 'has AAAA address', record.address)
        return
    answer = dns.resolver.query(hostname, 'CNAME')
    if answer.rrset is not None:
        record = answer[0]
        cname = record.address
        print(indent, hostname, 'is a CNAME alias for', cname) #?
        resolve_hostname(cname, indent)
    answer = dns.resolver.query(hostname, 'AAAA')
    if answer.rrset is not None:
        for record in answer:
            print(indent, hostname, 'has AAAA address', record.address)
        return
    answer = dns.resolver.query(hostname, 'CNAME')
    if answer.rrset is not None:
        record = answer[0]
        cname = record.address
        print(indent, hostname, 'is a CNAME alias for', cname) #?
        resolve_hostname(cname, indent)
        return
    print(indent, 'ERROR: no A, AAAA, or CNAME records for', hostname)

def resolve_email_domain(domain):
    "For an email address `name@domain` find its mail server IP addresses."
    try:
        answer = dns.resolver.query(domain, 'MX', raise_on_no_answer=False)
    except dns.resolver.NXDOMAIN:
        print('Error: No such domain', domain)
        return
    if answer.rrset is not None:
        records = sorted(answer, key=lambda record: record.preference)
        for record in records:
            name = record.exchange.to_text(omit_final_dot=True)
            print('Priority', record.preference)
            resolve_hostname(name)
    else:
        print('This domain has no explicit MX records')
        print('Attempting to resolve it as an A, AAAA, or CNAME')
        resolve_hostname(domain)

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Find mailserver IP address')
    parser.add_argument('domain', help='domain that you want to send mail to')
    resolve_email_domain(parser.parse_args().domain)