How can I do DNS lookups in Python including referring to etc hosts

Question

dnspython will do my DNS lookups very nicely  but it entirely ignores the contents of  etc hosts   Is there a python library call which will do the right thing  ie check first in etc hosts  and only fall back to DNS lookups otherwise

User · Answer

Sounds like you don t want to resolve dns yourself  this might be the wrong nomenclature  dnspython appears to be a standalone dns client that will understandably ignore your operating system because its bypassing the operating system s utillities  We can look at a shell utility named getent to understand how the  debian 11 alike  operating system resolves dns for programs  this is likely the standard for all  nix like systems that use a socket implementation  see man getent s  quot hosts quot  section  which mentions the use of getaddrinfo  which we can see as man getaddrinfo and to use it in python  we have to extract some info from the data structures   import socket  def get ipv4 by hostname hostname         see  man getent     hosts         see  man getaddrinfo       return list          i          raw socket structure              4     internet protocol info              0     address         for i in          socket getaddrinfo              hostname              0    port  required                   if i 0  is socket AddressFamily AF INET    ipv4            ignore duplicate addresses with other socket types         and i 1  is socket SocketKind SOCK RAW          print get ipv4 by hostname  localhost    print get ipv4 by hostname  google com

User · Answer

The answer above was meant for Python 2  If you re using Python 3  here is the code    gt  gt  gt  import socket  gt  gt  gt  print socket gethostbyname  google com    8 8 8 8  gt  gt  gt

User · Answer

This code works well for returning all of the IP addresses that might belong to a particular URI  Since many systems are now in a hosted environment  AWS Akamai etc    systems may return several IP addresses  The lambda was  borrowed  from  Peter Silva   def get ips by dns lookup target  port None                   this function takes the passed target and optional port and does a dns         lookup  it returns the ips that it finds to the caller            param target   the URI that you d like to get the ip address es  for          type target    string          param port     which port do you want to do the lookup against           type port      integer          returns ips    all of the discovered ips for the target          rtype ips      list of strings              import socket      if not port          port   443      return list map lambda x  x 4  0   socket getaddrinfo       format target  port type socket SOCK STREAM     ips   get ips by dns lookup target  google com

User · Answer

The normal name resolution in Python works fine  Why do you need DNSpython for that  Just use socket s getaddrinfo which follows the rules configured for your operating system  on Debian  it follows  etc nsswitch conf    gt  gt  gt  print socket getaddrinfo  google com   80    10  1  6        2a00 1450 8006  63   80  0  0     10  2  17        2a00 1450 8006  63   80  0  0     10  3  0        2a00 1450 8006  63   80  0  0     10  1  6        2a00 1450 8006  68   80  0  0     10  2  17        2a00 1450 8006  68   80  0  0     10  3  0        2a00 1450 8006  68   80  0  0     10  1  6        2a00 1450 8006  93   80  0  0     10  2  17        2a00 1450 8006  93   80  0  0     10  3  0        2a00 1450 8006  93   80  0  0     2  1  6        209 85 229 104   80     2  2  17        209 85 229 104   80     2  3  0        209 85 229 104   80     2  1  6        209 85 229 99   80     2  2  17        209 85 229 99   80     2  3  0        209 85 229 99   80     2  1  6        209 85 229 147   80     2  2  17        209 85 229 147   80     2  3  0        209 85 229 147   80

User · Answer

list  map  lambda x  x 4  0   socket getaddrinfo          www example com   22 type socket SOCK STREAM      gives you a list of the addresses for www example com    ipv4 and ipv6

User · Answer

I found this way to expand a DNS RR hostname that expands into a list of IPs  into the list of member hostnames      usr bin python  def expand dnsname dnsname       from socket import getaddrinfo     from dns import reversename  resolver     namelist             expand hostname into dict of ip addresses     iplist   dict       for answer in getaddrinfo dnsname  80           ipa   str answer 4  0           iplist ipa    0       run through the list of IP addresses to get hostnames     for ipaddr in sorted iplist           rev name   reversename from address ipaddr            run through all the hostnames returned  ignoring the dnsname         for answer in resolver query rev name   PTR                name   str answer              if name    dnsname                    add it to the list of answers                 namelist append name                  break       if no other choice  return the dnsname     if len namelist     0          namelist append dnsname        return the sorted namelist     namelist   sorted namelist      return namelist  namelist   expand dnsname  google com    for name in namelist      print name   Which  when I run it  lists a few 1e100 net hostnames

User · Answer

I m not really sure if you want to do DNS lookups yourself or if you just want a host s ip  In case you want the latter       socket gethostbyname is depricated  prefer socket getaddrinfo  from man gethostbyname   The gethostbyname     gethostbyaddr           functions are obsolete   Applications should use getaddrinfo 3    getnameinfo 3     import socket print socket gethostbyname  localhost      result from hosts file print socket gethostbyname  google com      your os sends out a dns query

[python] How can I do DNS lookups in Python, including referring to /etc/hosts?

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