# Building a port scanner in python

![Building a port scanner in python](https://cdn.hashnode.com/res/hashnode/image/upload/v1680988442192/13b1e7e4-03f7-48e6-84c8-668cbf0e87b0.jpeg)

Like I mentioned in the previous post, I will be trying to build a basic port scanner based in python. I will be using knowledge regarding python that I regained not too long ago from a course! This won't be a spectacular port scanner like Nmap but it would be something functional that beginners could build :)I made use of the library called ****SOCKET****.Let's get into it, shall we? :)

* * *

> Import the needed libraries

    #!/bin/python3
    import sys
    import socket
    from datetime import datetime as dt
    #Helpful functions
    def nl():
     print('\n') #prints new line when function is called

*   ****sys**** for getting arguments input by the user.
*   ****socket**** for making a successful connection to the host.
*   ****dateTime****…..for….you know? DateTime purposes!

* * *

> Define the target

    #Define our target 
    if len(sys.argv) == 2: #Checkes if there are only 2 args entered 
     target = socket.gethostbyname(sys.argv[1]) #DNS 
    else:  
     nl()  
     print("Invalid number of arguments entered :(")  
     print("Syntax --> python3 portscanner.py <IP Address>")  nl()

*   If the number of arguments entered matches the number of arguments we require, we let the program continue
*   Else, we alert the user that the input was invalid

* * *

> Create a banner (optional)

    #Add a pretty banner 
    nl() 
    print("~" * 50) 
    print("Scanning host ~> {}".format(target)) 
    print("Time started: {}".format(dt.now())) 
    print("~" * 50) 
    nl()

* * *

> Create a try statement to scan ports on the target machine

    try:
     for port in range (21,81):
      s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) #Declaring needed methods to a variable for later use
      socket.setdefaulttimeout(1) #Ends connection if a port does not respond in 1 second
      result = s.connect_ex((target, port)) #Returns an error indicator; Open port = 0 Closed port = 1
      #print("Checking port {}".format(port))
      if result == 0:
       print("<~ Port {} is open and unfiltered ~>".format(port))
       #nl()
      s.close

*   Try’s to connect to all the ports in rage (21,81) \[this can be changed to the port that you prefer\]
*   Sets default timeout to 1 second to avoid delays
*   Connects to the target using the IP the user entered and the port in the for loop range

* * *

Create exceptions for the program
---------------------------------

    except KeyboardInterrupt: #If the user interupts the program, the following will occur  
     print("<~ Terminating Scan ~>")  
     sys.exit()  
    except socket.gaierror: #If the hostname could not be resolved, the following will occur  
     print("<~ !Hostname could not be resolved! ~>")  
     sys.exit()   
    except socket.gaierror: #If no successful connection could be made with the host, the following will occur  
     print("<~ !Couldn't connect to server! ~>")  
     sys.exit()

*   If the user stops the program, it will terminate
*   If the program is unable to resolve the hostname, it will terminate
*   If the program cant initiate a successful connection with the server, it will terminate

* * *

> Final product

I made some changes to the look of the program and added a place holder to show how long the program ran for.

![Building a port scanner in python](https://cdn.hashnode.com/res/hashnode/image/upload/v1680988444301/003fd919-a22e-475e-bc2a-493ea4a1d084.png)