Merging a Python script's subprocess' stdout and stderr while keeping them distinguishable

Question

I would like to direct a python script's subprocess' stdout and stdin into the same file. What I don't know is how to make the lines from the two sources distinguishable? (For example prefix the lines from stderr with an exclamation mark.)

In my particular case there is no need for live monitoring of the subprocess, the executing Python script can wait for the end of its execution.

question from:https://stackoverflow.com/questions/6809590/merging-a-python-scripts-subprocess-stdout-and-stderr-while-keeping-them-disti

Answer 1

tsk = subprocess.Popen(args,stdout=subprocess.PIPE,stderr=subprocess.STDOUT)

subprocess.STDOUT is a special flag that tells subprocess to route all stderr output to stdout, thus combining your two streams.

btw, select doesn't have a poll() in windows. subprocess only uses the file handle number, and doesn't call your file output object's write method.

to capture the output, do something like:

logfile = open(logfilename, 'w')

while tsk.poll() is None:
    line = tsk.stdout.readline()
    logfile.write(line)