detect suprocess interaction

[Robin Becker]

Nick Craig-Wood wrote:
> Robin Becker <robin at reportlab.com> wrote:
>>  I'm using subprocess to carry out svn commands (probably should use the svn api 
.............
>>
>>  Clearly I need to supply some kind of input filelike object, but is this sort of 
>>  thing possible.
> 
> Yes it is possible, but if you try it you'll find you'll need to
> implement the fileno() method of file objects which is asked to return
> an OS file handle.  This is obviously a problem!
> 

yes I figured I might have to do something low level, but it's not 
terribly obvious that I can detect the read at the other end ie normally 
we seem to detect when output is available, not when a write is required 
ie I might be able to write to the input of my command even if the 
command won't read.

> In general subprocess isn't really designed for interactive
> processes like the above.  You'll find it much easier to use pexpect
> for interactive stuff.
> 
> Note that svn has its own devious ways of finding a terminal to ask
> the user for the password, eg...
> 
> $ svn ls svn+ssh://user@127.0.0.1/svn </dev/null >/dev/null 2>&1
> Password: 
> 
> I don't know exactly how it does that but I suspect it is to do with
> the controlling terminal...
> 
> On my system
> 
> $ setsid svn ls svn+ssh://user@127.0.0.1/svn </dev/null >/dev/null 2>&1
> 
> Pops up a gui box asking for the password!
> 
> You can simulate the above with
> 
>   Popen(..., stdin=file(os.devnull,"r"), preexec_fn=os.setsid)
.....

this just makes life more interesting :)
-- 
Robin Becker