Python twisted reactor - address already in use

I'm following a tutorial http://www.raywenderlich.com/3932/how-to-create-a-socket-based-iphone-app-and-server for creating a sample using socket programming in Mac OS X enviromment.

I'm writing using post 80 for reactor.listenTCP(80, factory). When I run the server.py file, getting an error:

File "server.py", line 10, in <module>
    reactor.listenTCP(6, factory)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/twisted/internet/posixbase.py", line 436, in listenTCP
    p.startListening()
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/twisted/internet/tcp.py", line 641, in startListening
    raise CannotListenError, (self.interface, self.port, le)
twisted.internet.error.CannotListenError: Couldn't listen on any:80: [Errno 48] Address already in use.

Source code is as follow:

from twisted.internet.protocol import Factory, Protocol
from twisted.internet import reactor

class IphoneChat(Protocol):
    def connectionMade(self):
        self.factory.clients.append(self)
        print "clients are ", self.factory.clients

    def connectionLost(self, reason):
        self.factory.clients.remove(self)

factory = Factory()
factory.protocol = IphoneChat
factory.clients = []
reactor.listenTCP(80, factory)
print "Iphone Chat server started"
reactor.run()

If I'm using another port no like 6 etc, it is working fine. I just wanted to know, how can I use port 80 for the same application.

Open Activity Monitor, search for Python and kill the process. You probably messed up with closing a server once.

I encountered this issue too, actually, just now.

Here is what I did:

MacBook-Air:Desktop user$ sudo lsof -i:80
COMMAND  PID USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
Python  1276 root    3u  IPv4 ******      0t0  TCP *:http (LISTEN)
MacBook-Air:Desktop user$ sudo kill 1276
MacBook-Air:Desktop user$ sudo python server.py 
Iphone Chat server started

Then everything goes well.

For me the issue was that apache was already listening on port 80. Seems like a lot of people google through this post and other ones with this issue but I don't see this particular answer offered. It was what worked for me so I thought that I would add to it in case it helps: Running Mac/Mavericks but the issue would occur on any other system where Apache runs by default ... or one might forget it's running.

Did

sudo lsof -i TCP:80 | grep LISTEN

Got

httpd      20 root    4u  IPv6 0x1d12a12e12345b12      0t0  TCP *:http (LISTEN)
httpd     109 _www    4u  IPv6 0x1d12a12e12345b12      0t0  TCP *:http (LISTEN)
httpd     437 _www    4u  IPv6 0x1d12a12e12345b12      0t0  TCP *:http (LISTEN)
httpd     438 _www    4u  IPv6 0x1d12a12e12345b12      0t0  TCP *:http (LISTEN)
httpd     439 _www    4u  IPv6 0x1d12a12e12345b12      0t0  TCP *:http (LISTEN)

did