oscartheduck wrote:
> I have a small script for doing some ssh stuff for me. I could have
> written it as shell script, but wanted to improve my python skills
> some.
>
> RIght now, I'm not catching a syntax error as I'd like to.
>
> Here's my code:
>
> #!/usr/bin/env python
> import sys
> import os
>
> port = input("Please enter a port to connect on. If you're unsure or
> just want the default of port 2024 just hit enter -- ")
>
>
> try:
> if port > 65535:
> print "That's not a valid port number, sorry. Between 0 and 65535
> is cool."
> sys.exit()
> else:
> cmd = 'su root -c "/usr/sbin/sshd -p %s"' % port
> except SyntaxError:
> cmd = 'su root -c "/usr/sbin/sshd -p 2024;exit"'
>
> os.system(cmd)
>
>
> I'm under the impression that the except should catch the syntax error
> and execute the "default" command, but hitting enter at the input
> value doesn't lead to that. Any ideas what's going wrong?
>
Yes. SyntaxError is raised when the interpreter is compiling the Python
into byetcodes ready for execution. This *can* happen at run time, but
usually it's when you are importing a module and so it gets
transmogrified into an ImportError, though you can trigger it with, for
example, eval:
>>> eval("print < m s q")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<string>", line 1
print < m s q
^
SyntaxError: invalid syntax
>>>
However, if you run your program and give it an invalid port number
surely the resulting traceback would *tell* you what exception you need
to trap if you used a %d substituion rather than a %s. Since pretty much
anything is valid for a %s substitution the problem is that you will be
calling os.system() on a command with a non-numeric port number and not
catching the resulting exception.
Using input(), by the way, is a recipe for disaster with non-trustworthy
users. I'd much prefer to use raw_input() and convert explicitly to integer.
The easiest way to proceed would then be to perform sensible error
checking on the port number before proceeding:
port = raw_input("Port # (enter for 2204 default: ")
if port == "":
port = 2204
try:
port = int(port)
except ValueError:
raise ValueError("Port number must be numeric")
or something like that. Really you should be in a loop which terminated
when you get an acceptable port number.
regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden
Recent Ramblings http://holdenweb.blogspot.com
--
http://mail.python.org/mailman/listinfo/python-list
