Python Cookbook

Writing a TCP Client

Credit: Luther Blissett

Problem

You want to connect to a socket on a remote machine.

Solution

Assuming you’re using the Internet to communicate:

import socket

# Create a socket
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Connect to the remote host and port
sock.connect((remote_host, remote_port))

# Send a request to the host
sock.send("Why don't you call me any more?\r\n")

# Get the host's response, no more than, say, 1,024 bytes
response_data = sock.recv(1024)

# Terminate
sock.close(  )

Discussion

The remote_host string can be either a domain name, such as 'www.python.org', or a dotted quad, such as '194.109.137.226'. The remote_port variable is an integer, such as 80 (the default HTTP port). If an error occurs, the failing operation raises an exception of the socket.error class. The socket module does not give you the ability to control a timeout for the operations you attempt; if you need such functionality, download the timeoutsocket module from http://www.timo-tasi.org/python/timeoutsocket.py, place it anywhere on your Python sys.path, and follow the instructions in the module itself.

If you want file-like objects for your network I/O, you can build one or more with the makefile method of the socket object, rather than using the latter’s send and receive methods directly. You can independently close the socket object and each file obtained from it, without affecting any other (or you can let garbage collection close them for you). For example, if sock is a connected socket object, you could write:

sockOut = sock.makefile('wb')
sockIn = sock.makefile('r')
sock.close(  )
print >> sockOut, "Why don't you call me any more?\r"
sockOut.close(  )
for line in sockIn:       # Python 2.2 only; 'in sockin.xreadlines(  )' in 2.1
    print 'received:', line,

See Also

Recipe 10.3; documentation for the standard library module socket in the Library Reference; the timeout modifications at http://www.timo-tasi.org/python/timeoutsocket.py, although these will likely be incorporated into Python 2.3; Perl Cookbook Recipe 17.1.