[GRASS-dev] python scripts and standard input

[Glynn Clements]

Massimo Di Stefano wrote:

> actually i'm using :
> 
> out = subprocess.Popen(['m.proj', '-o'], stdout=subprocess.PIPE,  stdin=subprocess.PIPE).communicate("%s %s" % (x,y))[0]

That will work on Unix, but Windows will complain due to the lack of
the .exe suffix. You can use grass.Popen() to get around that.

> This topic, maybe is good to discuss a problem i'm having about subprocess,
> please apologize me if it is OT, tell me to open a new thread.
> 
> The error i'm having is strictly connected with subprocess and how grass handle it.
> The weird is that the error i'm having comes up only on OSX while on linux all works fine.
> 
> this the error log  :

>   File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/subprocess.py", line 663, in communicate
>     stdout = self.stdout.read()
> IOError: [Errno 4] Interrupted system call

This appears to be a bug either in Python's read() method for pipes or
in Python's subprocess module. The underlying read() is failing with
EINTR, which can happen if a signal is received during a blocking
system call.

Normally, you would configure the signal handler to resume any system
calls (unless you specifically want it to interrupt blocking calls,
e.g. implementing a timeout by setting a timer and having SIGALRM
interrupt the system call).

In this case, I would expect the code to just try again, rather than
raising an exception. EINTR and EAGAIN are "transient" errors, in that
a subsequent attempt will typically succeed.

-- 
Glynn Clements <glynn at gclements.plus.com>