Python program crashes when it cannot connect to host

[darthsabbath]

Hi, all,

I've recently begun work on my first real programming project... a console based email client with a UI based somewhat on Pine (a la Nano being based on Pico)... but with features closer to a standard email client like Thunderbird or Eudora... especially no need for an external agent such as fetchmail. Yeah, I know there's a million email clients, but damnit, I have an itch to scratch. ;-)

Well... I'm fairly new at this programming thing, and I may be missing something totally obvious here... well, let me explain first.

One of the modules I'm creating is a session manager that wraps around the Python implementations of POP3, IMAP, and SMTP to keep them all in one tidy place. I barely have any code to show for it right now, at least in a useable form... it's just basically being built from the ground up... but take this portion from the POP3 manager...


def ConnectHost(self):
print "Connecting to host %s" % self.host
self.session = POP3(self.host, self.port)
print "Sending username %s" % self.login
self.session.user(self.login)
print "Login successful!\n Sending password!"
self.session.pass_(self.pwd)
print "Login complete!"


Please excuse the simple nature of this... I want to get the basics working before moving on. Anyway.... Everything's all fine and dandy until, say I enter in an invalid hostname... then the program goes down the tubes:


Traceback (most recent call last):
File "/home/pwm/pyne-project/pyne.py", line 9, in -toplevel-
p.ConnectHost()
File "/home/pwm/pyne-project/sessionmgr.py", line 15, in ConnectHost
self.session = POP3(self.host, self.port)
File "/usr/lib/python2.4/poplib.py", line 84, in __init__
for res in socket.getaddrinfo(self.host, self.port, 0, socket.SOCK_STREAM):
gaierror: (-2, 'Name or service not known')


Obviously this won't do... is there any way to catch this? I've looked into try/catch/except statements and am not sure how I would implement them in this situation. I know there's a Python lib out there that would allow me to ping the host to make sure it's reachable, but Python also crashes on an invalid username or password....


Traceback (most recent call last):
File "/home/pwm/pyne-project/pyne.py", line 9, in -toplevel-
p.ConnectHost()
File "/home/pwm/pyne-project/sessionmgr.py", line 19, in ConnectHost
self.session.pass_(self.pwd)
File "/usr/lib/python2.4/poplib.py", line 202, in pass_
return self._shortcmd('PASS %s' % pswd)
File "/usr/lib/python2.4/poplib.py", line 165, in _shortcmd
return self._getresp()
File "/usr/lib/python2.4/poplib.py", line 141, in _getresp
raise error_proto(resp)
error_proto: -ERR invalid user name or password.


Any help would be appreciated on how I could catch these problems.... I don't even need a detailed explanation... if someone could point me to a solution I'd be happy to pursue it on my own.

Maybe I'm just being dense this weekend. :-)

Phil

[amohanty]

I would suggest each module handle its own errors, so that this:
self.session = POP3(self.host, self.port)

should do the error handling for server connectivity, similarly for user authentication, the name validation should be handled by the:
self.session.user(self.login)

which means in botch cases the POP3 class. I havent used it so cant help you there. Also you will have to go through the source/docs and find out what errors are raised by the methods you mentioned above and then:

try:
sess = POP3...
sess.user...
sess.pass....
except ErrorRaisedByPOP2Ctor:
print err
except ErrorRaisedBysession.user:
print err
...
...
else:
cleanup()

HTH

[ow50]

Obviously this won't do... is there any way to catch this? I've looked into try/catch/except statements and am not sure how I would implement them in this situation.
gaierror is explained here (http://docs.python.org/lib/module-socket.html).

So, something like this might do:
import socket
(...)
try:
self.session = POP3(self.host, self.port)
except socket.herror, detail:
print (...)
except socket.gaierror, detail:
print (...)
except socket.timeout, detail:
print (...)

Catch every possible error and print an error message suitable for the error catched.

[darthsabbath]

Awesome... thanks for the help guys. I was thinking it had to be something along those lines, but I'll be damned if I knew what. :-)

Phil