Can anyone explain a part of a telnet client code to me..

[Jia Lu]

Hello
I have a program that can telnet to a host.
But I cannot understand from [for c in data] part, can anyone explain
it to me?
Thank you very much.

[code]
import sys, posix, time
from socket import *

BUFSIZE = 1024

# Telnet protocol characters

IAC = chr(255) # Interpret as command
DONT = chr(254)
DO = chr(253)
WONT = chr(252)
WILL = chr(251)

def main():
# Get hostname from param
host = sys.argv[1]
try:
# Get ip from hostname
hostaddr = gethostbyname(h ost)
except error:
sys.stderr.writ e(sys.argv[1] + ': bad host name\n')
sys.exit(2)
# Check param[2] as type of protocol
if len(sys.argv) 2:
servname = sys.argv[2]
else:
# default use telnet
servname = 'telnet'
# If got servname as port num
if '0' <= servname[:1] <= '9':
# cast port num from str to int
port = eval(servname)
else:
try:
# Get port num by service name
port = getservbyname(s ervname, 'tcp')
except error:
sys.stderr.writ e(servname + ': bad tcp service name\n')
sys.exit(2)
# Create a tcp socket
s = socket(AF_INET, SOCK_STREAM)
# Connect to server
try:
s.connect((host , port))
except error, msg:
sys.stderr.writ e('connect failed: ' + repr(msg) + '\n')
sys.exit(1)
# Fork a proccess
pid = posix.fork()
#
if pid == 0:
# child -- read stdin, write socket
while 1:
line = sys.stdin.readl ine()
s.send(line)
else:
# parent -- read socket, write stdout
iac = 0 # Interpret next char as command
opt = '' # Interpret next char as option
while 1:
data = s.recv(BUFSIZE)
# if recv nothing then Exit program
if not data:
# EOF; kill child and exit
sys.stderr.writ e( '(Closed by remote host)\n')
# Call posix function kill and send signal 9 to child
posix.kill(pid, 9)
sys.exit(1)
cleandata = ''
for c in data:
if opt:
print ord(c)
s.send(opt + c)
opt = ''
elif iac:
iac = 0
if c == IAC:
cleandata = cleandata + c
elif c in (DO, DONT):
if c == DO: print '(DO)',
else: print '(DONT)',
opt = IAC + WONT
elif c in (WILL, WONT):
if c == WILL: print '(WILL)',
else: print '(WONT)',
opt = IAC + DONT
else:
print '(command)', ord(c)
elif c == IAC:
iac = 1
print '(IAC)',
else:
cleandata = cleandata + c
sys.stdout.writ e(cleandata)
sys.stdout.flus h()
try:
main()
except KeyboardInterru pt:
pass

[Gabriel Genellina]

En Sun, 11 Feb 2007 00:48:57 -0300, Jia Lu <Ro*****@gmail. comescribió:

I have a program that can telnet to a host.
But I cannot understand from [for c in data] part, can anyone explain
it to me?

data is the received string.
The for statement is used to iterate over a sequence; a string is
considered a sequence of characters, so it iterates over all the
characters in the string, one by one.

pydata = "Hello"
pyfor c in data:
.... print c, ord(c)
....
H 72
e 101
l 108
l 108
o 111
py>

--
Gabriel Genellina