embedding: how do I redirect print output?

Thomas Jollans t at jollybox.de
Tue Jul 5 16:18:20 CEST 2011


On 07/05/2011 02:50 PM, Ulrich Eckhardt wrote:
> I'm trying to add some scripting capabilities to an application. Since it is 
> a GUI application, I need some way to display output from Python. For 3.x, 
> where "print" is a function, I'd just exchange this function with one that 
> redirects the output to a log window, right.
> 
> However, I'm using 2.6 here, where that can't work. So, what I was thinking 
> was to redirect "sys.stdout" and "sys.stderr" to a log window and possibly 
> replace "sys.stdin" with something that causes meaningful errors if some 
> code tries to use it, but that last point is just icing on the cake.
> 
> What seems cumbersome is that I'll need to write something that supports the 
> file interface using C, which is still a bit awkward. I'm wondering, isn't 
> there an easier way to achieve this? How would you do it?

You can mess with low-level file descriptors. Example:

# create new stdout:
fout = file('out.txt', 'w')

# close stdout (fd 1)
import os
os.close(1)

# use fout as new stdout
os.dup2(fout.fileno(), 1)

# test. This will end up in out.txt
print "Testing."

# do the same for stdin (0) and stderr (2)

# - EOF -

However, I suggest you consider isolating your scripts from you main
program and run them in a separate interpreter. You can provide dummy
modules that communicate with your application via sockets to the
scripts. Setting the standard files in the child process is easy: the
Popen constructor takes stdin/stdout/stderr arguments.

-T



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