怎样检验域名是否有效

nslookup example.com

import dns.resolver

def check_dns(domain):
    try:
        answers = dns.resolver.resolve(domain, 'A')
        return True
    except dns.resolver.NXDOMAIN:
        return False
    except dns.resolver.NoAnswer:
        return False
    except dns.resolver.Timeout:
        return False

print(check_dns('example.com'))

curl -I http://example.com

import requests

def check_http(domain):
    try:
        response = requests.head(f'http://{domain}', timeout=5)
        return response.status_code == 200
    except requests.RequestException:
        return False

print(check_http('example.com'))

whois example.com

import whois

def check_whois(domain):
    try:
        w = whois.whois(domain)
        return w.domain_name is not None
    except Exception:
        return False

print(check_whois('example.com'))