[py-dev] Request for enhancing Exception handling in execnet

[Walter Dörwald]

Gerard Petersen wrote:
> Guido,
> 
> Thanx for the code snippet. Initially I wanted to keep the code that goes 
> remote as clean as possible (somebody told me ... ;-) but 
> the code you came up with does seem good. 
> 
> The actual issue is somewhat more elaborate. I also have remote functions that 
> read files, and a predicatble situation is that a file might not be there 
> remotely. Since this is a possibiltity and not an exception as such, (next to 
> a "permission denied" which is). There is also the possibility to return an 
> error value along all the time. You then would still need some error handling 
> remotely but the last line in your function would be something like "return 
> contents, error".
> "Error" containing a level from zero upwards. I'll see if I can combine a 
> setup like that with the "isinstance" function.
> 
> More on  the way, Thanx guys!!

You might take a look at the ll.url module which is part of XIST 
(available from: http://www.livinglogic.de/Python/Download.html

ll.url implements an ssh URL scheme which supports all file operations 
remotely:

 >>> from ll import url
 >>> u = url.URL("ssh://root@www.example.org/~/")
 >>> u.listdir(context=url.Context())
[URL('.bash_history'),
  URL('.profile'),
  URL('.bashrc'),
...

 >>> u = url.URL("ssh://root@www.example.org/~/.bash_history")
 >>> f = u.open("rb", context=url.Context())
 >>> f.readline()
'/etc/init.d/tomcat stop\n'
 >>> f.readline()
'ps waux | grep tomcat\n'

It mirrors exceptions locally:

 >>> u = url.URL("ssh://root@www.example.org/~/does-not-exist")
 >>> f = u.open("rb", context=url.Context())
[...]
IOError: [Errno 2] No such file or directory: '/root/does-not-exist'

(of course this only works for builtin exceptions)

And of course ll.url uses py.execnet for communicating with the remote host.

Hope that helps!

Servus,
    Walter