Stealth Port Scanner (Scapy and Python)

#! /usr/bin/python
from logging import getLogger, ERROR # Import Logging Things
getLogger("scapy.runtime").setLevel(ERROR) # Get Rid if IPv6 Warning
from scapy.all import * # The One and Only Scapy
import sys
from datetime import datetime # Other stuff
from time import strftime

try:
    target = raw_input("[*] Enter Target IP Address: ") # Get Target Address
    min_port = raw_input("[*] Enter Minumum Port Number: ") # Get Min. Port Num.
    max_port = raw_input("[*] Enter Maximum Port Number: ") # Get Max. Port Num.
    try:
        if int(min_port) >= 0 and int(max_port) >= 0 and int(max_port) >= int(min_port): # Test for valid range of ports
            pass
        else: # If range didn't raise error, but didn't meet criteria
            print "\n[!] Invalid Range of Ports"
            print "[!] Exiting..."
            sys.exit(1)
    except Exception: # If input range raises an error
        print "\n[!] Invalid Range of Ports"
        print "[!] Exiting..."
        sys.exit(1)
except KeyboardInterrupt: # In case the user wants to quit
    print "\n[*] User Requested Shutdown..."
    print "[*] Exiting..."
    sys.exit(1)

ports = range(int(min_port), int(max_port)+1) # Build range from given port numbers
start_clock = datetime.now() # Start clock for scan time
SYNACK = 0x12 # Set flag values for later reference
RSTACK = 0x14

def checkhost(ip): # Function to check if target is up
    conf.verb = 0 # Hide output
    try:
        ping = sr1(IP(dst = ip)/ICMP()) # Ping the target
        print "\n[*] Target is Up, Beginning Scan..."
    except Exception: # If ping fails
        print "\n[!] Couldn't Resolve Target"
        print "[!] Exiting..."
        sys.exit(1)

def scanport(port): # Function to scan a given port
    try:
        srcport = RandShort() # Generate Port Number
        conf.verb = 0 # Hide output
        SYNACKpkt = sr1(IP(dst = target)/TCP(sport = srcport, dport = port, flags = "S")) # Send SYN and recieve RST-ACK or SYN-ACK
        pktflags = SYNACKpkt.getlayer(TCP).flags # Extract flags of recived packet
        if pktflags == SYNACK: # Cross reference Flags
            return True # If open, return true
        else:
            return False # If closed, return false
        RSTpkt = IP(dst = target)/TCP(sport = srcport, dport = port, flags = "R") # Construct RST packet
        send(RSTpkt) # Send RST packet
    except KeyboardInterrupt: # In case the user needs to quit
        RSTpkt = IP(dst = target)/TCP(sport = srcport, dport = port, flags = "R") # Built RST packet
        send(RSTpkt) # Send RST packet to whatever port is currently being scanned
        print "\n[*] User Requested Shutdown..."
        print "[*] Exiting..."
        sys.exit(1)

checkhost(target) # Run checkhost() function from earlier
print "[*] Scanning Started at " + strftime("%H:%M:%S") + "!\n" # Confirm scan start

for port in ports: # Iterate through range of ports
    status = scanport(port) # Feed each port into scanning function
    if status == True: # Test result
        print "Port " + str(port) + ": Open" # Print status

stop_clock = datetime.now() # Stop clock for scan time
total_time = stop_clock - start_clock # Calculate scan time
print "\n[*] Scanning Finished!" # Confirm scan stop
print "[*] Total Scan Duration: " + str(total_time) # Print scan time