Deepak Kumar Deepak Kumar - 28 days ago 5
Python Question

Getting output of a process at runtime

I am using a python script to run a process using

subprocess.Popen
and simultaneously store the output in a text file as well as print it on the console. This is my code:

result = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE)
for line in result.stdout.readlines(): #read and store result in log file
openfile.write("%s\n" %line)
print("%s" %line)


Above code works fine, but what it does is it first completes the process and stores the output in result variable. After that for loop stores the output as well as print it.

But i want the output at runtime (as my process can take hours to complete, i don't get any output for all these hours).

So is there any other function that gives me the output dynamically (at runtime), means as soon as the process gives first line, it should get printed.

Answer

The problem here is that .readlines() gets the entire output before returning, as it constructs a full list. Just iterate directly:

for line in result.stdout:
    print line