Funnel lets you capture the stdout and stderr of a Python script into a simple list for later processing.

Take, for example, this demo_output.py script:

#!/usr/bin/env python

import os
import sys

print('Hello!')
sys.stderr.write('Multi-line\nError!\n')

It could have its output captured and validated like so:

#!/usr/bin/env python

import funnel

with funnel.capture_output() as out:
    execfile('demo_output.py')

result = out.get_output()

assert result == [
    ('stdout', 'Hello!'),
    ('stderr', 'Multi-line'),
    ('stderr', 'Error!')]

The resultant list is very human-readable; each line gets its own entry in the list and notes its source.

Funnel can also write the combined and labeled output to a file:

#!/usr/bin/env python

import funnel

with funnel.redirect_output_to_file('demo_output.log'):
    execfile('demo_output.py')

The above would result in the file demo_output.log containing the following lines:

[stdout] Hello!
[stderr] Multi-line
[stderr] Error!

Imagine, if you will, the following scenario:

#!/usr/bin/env python

import os
import sys

def load_file():
    sys.stderr.write("ERROR: I should raise an error, but I'm badly written!\n")

sys.stdout.write('Loading file...')
load_file()
sys.stdout.write('done\n')

Normally, you'd expect to see the following output in the console:

Loading file...ERROR: I should raise an error, but I'm badly written!
done

With funnel, the output looks a bit nicer:

[stderr] ERROR: I should raise an error, but I'm badly written!
[stdout] Loading file...done

The "Loading file" line is appended to the output when the line is completed. If the line is never completed, it is written out when funnel is cleaned-up.