Port Scanner scipts in Python

#!/usr/bin/python

import socket,sys,time,datetime,argparse,os
flag = 0  # we're gonna use this flag later. Just keep it in mind
os.system('clear') # Clear the console window
line = "+" * 80 # Just a fancy line consisting '+'
desc = line+'''\nA Simple port scanner that works!! (c) digitz.org
	Example usage: python port_scanner.py example.com 1 1000
	The above example will scan the host \'example.com\' from port 1 to 1000
	To scan most common ports, use: python port_scanner.py example.com\n'''+line+"\n"
	# Just a description about the script and how to use it
 
# I would suggest you to read about "argparse", it comes in handy
# when you want to parse arguments 
parser = argparse.ArgumentParser(description = desc, formatter_class=argparse.RawTextHelpFormatter)
parser.add_argument('host', metavar='H', help='Host name you want to scan')
parser.add_argument('startport', metavar='P1', nargs='?', help='Start scanning from this port')
parser.add_argument('endport', metavar='P2', nargs='?',help='Scan until this port')
args = parser.parse_args()
 
host = args.host # The host name to scan for open ports
ip = socket.gethostbyname(host) # Converts the host name into IP address 
 
# args.startpoint corresponds to the first port we will scan
# args.endport corresponds to the last port
 
# Here, we're checking if both starting port and ending port is defined
# If it is not defined, we will do a scan over most popular TCP ports. 
if (args.startport) and args.endport :
	# If this condition is true, the script will scan over this port range
	start_port = int(args.startport)
	end_port = int(args.endport)
else:
	# In this case, the script will scan the most common ports.
	# that is, if you did not give any ports as argument.
	flag = 1
 
open_ports = []  # This list is used to hold the open ports
 
# This dictionary contains the most popular ports used
# You can add ports here. 
# The key is the port number and the values is the service used by that port
common_ports = {
 
	'21': 'FTP',
	'22': 'SSH',
	'23': 'TELNET',
	'25': 'SMTP',
	'53': 'DNS',
	'69': 'TFTP',
	'80': 'HTTP',
	'109': 'POP2',
	'110': 'POP3',
	'123': 'NTP',
	'137': 'NETBIOS-NS',
	'138': 'NETBIOS-DGM',
	'139': 'NETBIOS-SSN',
	'143': 'IMAP',
	'156': 'SQL-SERVER',
	'389': 'LDAP',
	'443': 'HTTPS',
	'546': 'DHCP-CLIENT',
	'547': 'DHCP-SERVER',
	'995': 'POP3-SSL',
	'993': 'IMAP-SSL',
	'2086': 'WHM/CPANEL',
	'2087': 'WHM/CPANEL',
	'2082': 'CPANEL',
	'2083': 'CPANEL',
	'3306': 'MYSQL',
	'8443': 'PLESK',
	'10000': 'VIRTUALMIN/WEBMIN'
}
 
starting_time = time.time() # Get the time at which the scan was started
print "+" * 40
print "\tSimple Port Scanner..!!!"
print "+" * 40
 
if (flag): # The flag is set, that means the user did not provide any ports as argument
	print "Scanning for most common ports on %s" % (host)
else:
	# The user did specify a port range to scan
	print "Scanning %s from port %s - %s: " % (host, start_port, end_port)
print "Scanning started at %s" %(time.strftime("%I:%M:%S %p"))
 
 
# This is the function that will connect to a port and will check
# if it is open or closed
def check_port(host, port, result = 1):
	# The function takes 3 arguments
	# host : the IP to scan
	# port : the port number to connect
	try:
		# Creating a socket object named 'sock'
		sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
		# Setting socket timeout so that the socket does not wait forever to complete  a connection
		sock.settimeout(0.5)
		# Connect to the socket
		# if the connection was successful, that means the port
		# is open, and the output 'r' will be zero
		r = sock.connect_ex((host, port))	
		if r == 0:
			result = r 
		sock.close() # closing the socket
	except Exception, e:
		pass
 
	return result # returns the result of the scan.
 
# This function reads the dictonary of ports and services and 
# Checks for the service name corresponding to a port.
def get_service(port):
	port = str(port) # converts the int to string
	if port in common_ports: # check if the port is available in the common ports dictionary
		return common_ports[port] # returns the service name if available
	else:
		return 0 # return 0 if no service is identified
 
 
try:
	print "Scan in progress.."
	print "Connecting to Port: ",
 
	if flag: # The flag is set, means the user did not give any port range
		for p in sorted(common_ports): # So we will scan the common ports. 
			sys.stdout.flush() # flush the stdout buffer.
			p = int(p)
			print p,	
			response = check_port(host, p) # call the function to connect to the port
			if response == 0: # The port is open
				open_ports.append(p) # append it to the list of open ports
			#if not p == end_port:
				sys.stdout.write('\b' * len(str(p))) # This is just used to clear the port number displayed. This is not important at all
	else:
		
		# The user did provide a port range, now we have to scan through that range 
		for p in range(start_port, end_port+1):
			sys.stdout.flush()
			print p,
			response = check_port(host, p) # Call the function to connect to the port 
			if response == 0: # Port is open
				open_ports.append(p) # Append to the list of open ports
			if not p == end_port:
				sys.stdout.write('\b' * len(str(p)))
 
	print "\nScanning completed at %s" %(time.strftime("%I:%M:%S %p"))
	ending_time = time.time()
	total_time = ending_time - starting_time # Calculating the total time used to scan
	print "=" * 40
	print "\tScan Report: %s" %(host)
	print "=" * 40
	if total_time == 60:
		total_time = str(round(total_time, 2))
		print "Scan Took %s seconds" %(total_time)
	else:
		total_time = total_time / 60
		print "Scan Took %s Minutes" %(total_time)
		
	if open_ports: # There are open ports available
		print "Open Ports: "
		for i in sorted(open_ports):
			service = get_service(i)
			if not service: # The service is not in the disctionary
				service = "Unknown service"
			print "\t%s %s: Open" % (i, service)
	else:
		# No open ports were found
		print "Sorry, No open ports found.!!"
 
except KeyboardInterrupt: # This is used in case the  user press "Ctrl+C", it will show the following error instead of a python's scary error
	print "You pressed Ctrl+C. Exiting "		
	sys.exit(1)