I weep! This code is only useful when security and portability are not concerns. Admittedly that's the case here, but for more general cases use subprocess for real. Here's the code:
cmd = 'vw --loss_function logistic --cache_file {} -b {} 2>&1'.format(
path_to_cache, b )
output = subprocess.check_output( '{} | tee /dev/stderr'.format( cmd ), shell = True )
What happen if path_to_cache contains a space, or other shell metacharacter? The documentation warns that 'shell = True' is a security hazard. And this isn't portable to a non-Unix OS.
A possibly better solution is:
output = subprocess.check_output(
["vw", "--loss_function", "logistic", "--cache_file",
path_to_cache, "-b", b,"],
stderr = subprocess.STDOUT)
This doesn't have the tee, which is exists "so [output] gets printed on screen while at the same time it goes to standard output and is captured."
Since that's important, another solution is:
p = subprocess.Popen(
["vw", "--loss_function", "logistic", "--cache_file",
path_to_cache, "-b", b,"],
stdout = subprocess.PIPE,
stderr = subprocess.STDOUT)
output = []
for line in p.stdout:
sys.stderr.write(line)
output.append(line)
if not p.wait(): raise AssertionError("There was an error")
I'm the first to admit that this is longer, which may be an important concern for some. I prefer the greatly reduced number of gotchas.
