Python subprocess readlines() hangs

Question

The task I try to accomplish is to stream a ruby file and print out the output. (NOTE: I don\'t want to print out everything at once)

Answer 1

Try this:

proc = Popen(command, bufsize=0, shell=True, stdout=PIPE, close_fds=True)
for line in proc.stdout:
    print line

print("This is most certainly reached!")

As others have noted, readline() will block when reading data. It will even do so when your child process has died. I am not sure why this does not happen when executing ls as in the other answer, but maybe the ruby interpreter detects that it is writing to a PIPE and therefore it will not close automatically.