Checking network connection

Question

I want to see if I can access an online API  but for that I need to have Internet access   How can I see if there s a connection available and active using Python

User · Answer

Taking Ivelin s answer and add some extra check as my router delivers its ip address 192 168 0 1 and returns a head if it has no internet connection when querying google com   import socket  def haveInternet        try            first check if we get the correct IP-Address or just the router s IP-Address         info   socket getaddrinfo  www google com   None  0          ipAddr   info 4  0          if ipAddr     192 168 0 1                return False     except          return False      conn   httplib HTTPConnection  www google com   timeout 5      try          conn request  HEAD                conn close           return True     except          conn close           return False

User · Answer

my favorite one  when running scripts on a cluster or not  import subprocess  def online timeout       try          return subprocess run                wget    -q    --spider    google com                timeout timeout           returncode    0     except subprocess TimeoutExpired          return False   this runs wget quietly  not downloading anything but checking that the given remote file exists on the web

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It will be faster to just make a HEAD request so no HTML will be fetched  Also I am sure google would like it better this way      try      import httplib except      import http client as httplib  def have internet        conn   httplib HTTPConnection  www google com   timeout 5      try          conn request  HEAD                conn close           return True     except          conn close           return False

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Perhaps you could use something like this   import urllib2  def internet on        try          urllib2 urlopen  http   216 58 192 142   timeout 1          return True     except urllib2 URLError as err           return False   Currently  216 58 192 142 is one of the IP addresses for google com  Change http   216 58 192 142 to whatever site can be expected to respond quickly    This fixed IP will not map to google com forever  So this code is not robust -- it will need constant maintenance to keep it working    The reason why the code above uses a fixed IP address instead of fully qualified domain name  FQDN  is because a FQDN would require a DNS lookup  When the machine does not have a working internet connection  the DNS lookup itself may block the call to urllib request urlopen for more than a second  Thanks to  rzetterberg for pointing this out     If the fixed IP address above is not working  you can find a current IP address for google com  on unix  by running    dig google com   trace      google com      300 IN  A   216 58 192 142

User · Answer

Just to update what unutbu said for new code in Python 3 2  def check connectivity reference       try          urllib request urlopen reference  timeout 1          return True     except urllib request URLError          return False   And  just to note  the input here  reference  is the url that you want to check  I suggest choosing something that connects fast where you live -- i e  I live in South Korea  so I would probably set reference to http   www naver com

User · Answer

A modern portable solution with requests   import requests  def internet           Detect an internet connection          connection   None     try          r   requests get  https   google com           r raise for status           print  Internet connection detected            connection   True     except          print  Internet connection not detected            connection   False     finally          return connection   Or  a version that raises an exception   import requests from requests exceptions import ConnectionError  def internet           Detect an internet connection          try          r   requests get  https   google com           r raise for status           print  Internet connection detected        except ConnectionError as e          print  Internet connection not detected            raise e

User · Answer

import urllib  def connected host  http   google com        try          urllib urlopen host          return True     except          return False    test print   connected  if connected   else  no internet       For python 3  use urllib request urlopen host

User · Answer

import requests and try this simple python code  def check internet        url    http   www google com       timeout   5     try              requests get url  timeout timeout          return True     except requests ConnectionError          return False

User · Answer

As an alternative to ubutnu s Kevin C answers  I use the requests package like this  import requests  def connected to internet url  http   www google com    timeout 5       try              requests head url  timeout timeout          return True     except requests ConnectionError          print  quot No internet connection available  quot       return False  Bonus  this can be extended to this function that pings a website  def web site online url  http   www google com    timeout 5       try          req   requests head url  timeout timeout            HTTP errors are not raised by default  this statement does that         req raise for status           return True     except requests HTTPError as e          print  quot Checking internet connection failed  status code  0   quot  format          e response status code       except requests ConnectionError          print  quot No internet connection available  quot       return False

User · Answer

Taking Six  answer I think we could simplify somehow  an important issue as newcomers are lost in highly technical matters   Here what I finally will use to wait for my connection  3G  slow  to be established once a day for my PV monitoring   Works under Pyth3 with Raspbian 3 4 2  from urllib request import urlopen from time import sleep urltotest http   www lsdx eu               my own web page nboftrials 0 answer  NO  while answer   NO  and nboftrials lt 10      try          urlopen urltotest          answer  YES      except          essai  NO          nboftrials  1         sleep 30           maximum running  5 minutes if reached I will try in one hour s time but its another bit of script

User · Answer

For my projects I use script modified to ping the google public DNS server 8 8 8 8  Using a timeout of 1 second and core python libraries with no external dependencies   import struct import socket import select   def send one ping to  8 8 8 8       ping socket   socket socket socket AF INET  socket SOCK RAW  socket getprotobyname  icmp       checksum   49410    header   struct pack   BBHHH   8  0  checksum  0x123  1     data   b BCDEFGHIJKLMNOPQRSTUVWXYZ       abcdefghijklmnopqrstuvwx     header   struct pack          BBHHH   8  0  checksum  0x123  1         packet   header   data    ping socket sendto packet   to  1      inputready         select select  ping socket           1 0     if inputready              raise Exception  No internet      or return False       address   ping socket recvfrom 2048     print address     or return True   send one ping     The select timeout value is 1  but can be a floating point number of choice to fail more readily than the 1 second in this example

User · Answer

This works for me in Python3 6  import urllib from urllib request import urlopen   def is internet                Query internet using python      return              try          urlopen  https   www google com   timeout 1          return True     except urllib error URLError as Error          print Error          return False   if is internet        print  Internet is active   else      print  Internet disconnected

User · Answer

If we can connect to some Internet server  then we indeed have connectivity  However  for the fastest and most reliable approach  all solutions should comply with the following requirements  at the very least   Avoid DNS resolution  we will need an IP that is well-known and guaranteed to be available for most of the time  Avoid application layer connections  connecting to an HTTP FTP IMAP service  Avoid calls to external utilities from Python or other language of choice  we need to come up with a language-agnostic solution that doesn t rely on third-party solutions   To comply with these  one approach could be to  check if one of the Google s public DNS servers is reachable  The IPv4 addresses for these servers are 8 8 8 8 and 8 8 4 4  We can try connecting to any of them  A quick Nmap of the host 8 8 8 8 gave below result    sudo nmap 8 8 8 8  Starting Nmap 6 40   http   nmap org   at 2015-10-14 10 17 IST Nmap scan report for google-public-dns-a google com  8 8 8 8  Host is up  0 0048s latency   Not shown  999 filtered ports PORT   STATE SERVICE 53 tcp open  domain  Nmap done  1 IP address  1 host up  scanned in 23 81 seconds  As we can see  53 tcp is open and non-filtered  If you are a non-root user  remember to use sudo or the -Pn argument for Nmap to send crafted probe packets and determine if a host is up  Before we try with Python  let s test connectivity using an external tool  Netcat    nc 8 8 8 8 53 -zv Connection to 8 8 8 8 53 port  tcp domain  succeeded   Netcat confirms that we can reach 8 8 8 8 over 53 tcp  Now we can set up a socket connection to 8 8 8 8 53 tcp in Python to check connection  import socket  def internet host  quot 8 8 8 8 quot   port 53  timeout 3        quot  quot  quot      Host  8 8 8 8  google-public-dns-a google com      OpenPort  53 tcp     Service  domain  DNS TCP       quot  quot  quot      try          socket setdefaulttimeout timeout          socket socket socket AF INET  socket SOCK STREAM  connect  host  port           return True     except socket error as ex          print ex          return False  internet    Another approach could be to send a manually crafted DNS probe to one of these servers and wait for a response  But  I assume  it might prove slower in comparison due to packet drops  DNS resolution failure  etc  Please comment if you think otherwise  UPDATE  1  Thanks to  theamk s comment  timeout is now an argument and initialized to 3s by default  UPDATE  2  I did quick tests to identify the fastest and most generic implementation of all valid answers to this question  Here s the summary    ls   py   sort -n   xargs -I   sh -c  echo      timeit sh    echo  defos py True 00 00 00 00 487  iamaziz py True 00 00 00 00 335  ivelin py True 00 00 00 00 105  jaredb py True 00 00 00 00 533  kevinc py True 00 00 00 00 295  unutbu py True 00 00 00 00 546  7h3rAm py True 00 00 00 00 032  And once more    ls   py   sort -n   xargs -I   sh -c  echo      timeit sh    echo  defos py True 00 00 00 00 450  iamaziz py True 00 00 00 00 358  ivelin py True 00 00 00 00 099  jaredb py True 00 00 00 00 585  kevinc py True 00 00 00 00 492  unutbu py True 00 00 00 00 485  7h3rAm py True 00 00 00 00 035  True in the above output signifies that all these implementations from respective authors correctly identify connectivity to the Internet  Time is shown with milliseconds resolution  UPDATE  3  Tested again after the exception handling change  defos py True 00 00 00 00 410  iamaziz py True 00 00 00 00 240  ivelin py True 00 00 00 00 109  jaredb py True 00 00 00 00 520  kevinc py True 00 00 00 00 317  unutbu py True 00 00 00 00 436  7h3rAm py True 00 00 00 00 030

User · Answer

You can just try to download data  and if connection fail you will know that somethings with connection isn t fine   Basically you can t check if computer is connected to internet  There can be many reasons for failure  like wrong DNS configuration  firewalls  NAT  So even if you make some tests  you can t have guaranteed that you will have connection with your API until you try

User · Answer

This might not work if the localhost has been changed from 127 0 0 1 Try   import socket ipaddress socket gethostbyname socket gethostname    if ipaddress   127 0 0 1       print  You are not connected to the internet    else      print  You are connected to the internet with the IP address of    ipaddress     Unless edited   your computers IP will be 127 0 0 1 when not connected to the internet  This code basically gets the IP address and then asks if it is the localhost IP address   Hope that helps

User · Answer

Best way to do this is to make it check against an IP address that python always gives if it can t find the website  In this case this is my code   import socket  print  website connection checker   while True      website   input  please input website         print         print socket gethostbyname website       if socket gethostbyname website      92 242 140 2           print  Website could be experiencing an issue Doesn t exist       else          socket gethostbyname website          print  Website is operational            print

User · Answer

Make sure your pip is up to date by running pip install --upgrade pip  Install the requests package using pip install requests        import requests     import webbrowser     url    quot http   www youtube com quot       timeout   6     try          request   requests get url  timeout timeout          print  quot Connected to the Internet quot           print  quot browser is loading url quot           webbrowser open url      except  requests ConnectionError  requests Timeout  as exception         print  quot poor or no internet connection  quot

User · Answer

Here s my version    import requests  try      if requests get  https   google com   ok          print  You re Online   except      print  You re Offline

User · Answer

I added a few to Joel s code       import socket time     mem1   0     while True          try                  host   socket gethostbyname  www google com    Change to personal choice of site                 s   socket create connection  host  80   2                  s close                   mem2   1                 if  mem2    mem1                       pass  Add commands to be executed on every check                 else                      mem1   mem2                     print   Internet is working    Will be executed on state change          except Exception as e                  mem2   0                 if  mem2    mem1                       pass                 else                      mem1   mem2                     print   Internet is down           time sleep 10   timeInterval for checking

User · Answer

Taking unutbu s answer as a starting point  and having been burned in the past by a  static  IP address changing  I ve made a simple class that checks once using a DNS lookup  i e   using the URL  https   www google com    and then stores the IP address of the responding server for use on subsequent checks   That way  the IP address is always up to date  assuming the class is re-initialized at least once every few years or so    I also give credit to gawry for this answer  which showed me how to get the server s IP address  after any redirection  etc     Please disregard the apparent hackiness of this solution  I m going for a minimal working example here      Here is what I have   import socket  try      from urllib2 import urlopen  URLError     from urlparse import urlparse except ImportError     Python 3     from urllib parse import urlparse     from urllib request import urlopen  URLError  class InternetChecker object       conn url    https   www google com        def   init   self           pass      def test internet self           try              data   urlopen self conn url  timeout 5          except URLError              return False          try              host   data fp  sock fp  sock getpeername           except AttributeError     Python 3             host   data fp raw  sock getpeername              Ensure conn url is an IPv4 address otherwise future queries will fail         self conn url    http        host 0  if len host     2 else                                      socket gethostbyname urlparse data geturl    hostname            return True    Usage example checker   InternetChecker   checker test internet

User · Answer

Try the operation you were attempting to do anyway  If it fails python should throw you an exception to let you know   To try some trivial operation first to detect a connection will be introducing a race condition  What if the internet connection is valid when you test but goes down before you need to do actual work

[python] Checking network connection

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