python: how to redirect file output to stream

Question

I am working on a GUI version of a executable file. The file have a option as

exefile --output output.txt

My task is not save to output.txt, but can use some information in the file to plot a graph? I have some idea to plot the graph using pyqtgraph. The thing is how to get it as a text stream? Any thoughts?

Second question is similar but little more difficult. The same executable file can also output to a .wav

exefile --outwav outwav.wav

Instead of saving a .wav file, how to plot it out, in some of "real-time" way? Many thanks.

Note:

1. My intention is to build a wrapper, and I don't have any control inside the executable file.

2. Ideally the executable file should run continuously, while I plot output/wave during the time

Answer 1

Assuming that:

• you are on a Unix platform (Linux, Mac OSX)
• the original exefile has no way to do what you want
• you don't want / can't modify exefile

The best option would be using a named pipe.

This works just like a temporary file, but doesn't hit the hard drive - everything happens in memory. It has several advantages over a temporary file:

• you're able to process several gigabytes per second, without trashing your disk I/O
• you avoid having to synchronize reads, having to be extra careful with EOF, and not really knowing when exefile has finished writing.
• you avoid filling up the filesystem.

You can use os.mkfifo to create a named pipe. Read from it just like you would read from a normal file.

Note that exefile will periodically I/O block if writing to the named pipe happens faster than your program reads. Similarly, your program will I/O block if reading faster than exefile writing.

Answer 2

I think the best way would be to write to temporary file and then read it where needed. It's very easy to do in python:

from tempfile import NamedTemporaryFile
f = NamedTemporaryFile() # this is file object you will read from
f.name # and here you can get it's name

# here is simple way to run your command
import os
exit_code = os.system("execfile --output %s" % (f.name,))
if not exit_code:
    data = f.read()
else:
    print "Oooops. exit code = %s" % (exit_code,)

Check doc for more info.