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I am trying to read from a process that produces long and time-consuming output. However, I want to catch it's output as and when it is produced. But using something like the following seems to be buffering the command's output, so I end up getting the output lines all at once:
p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, bufsize=0) for line in p.stdout: print line I am trying this on MacOS 10.5
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To capture the output of the subprocess. run method, use an additional argument named “capture_output=True”. You can individually access stdout and stderr values by using “output. stdout” and “output.
subprocess. Process class is not thread safe. The Concurrency and multithreading in asyncio section.
Popen is more general than subprocess. call . Popen doesn't block, allowing you to interact with the process while it's running, or continue with other things in your Python program. The call to Popen returns a Popen object.
subprocess. check_output() is the one that runs the command and returns the return value. If you want the output write your value to STDOUT and use check_output() to get the value.
The file iterator is doing some internal buffering on its own. Try this:
line = p.stdout.readline() while line: print line line = p.stdout.readline() You also need to make sure the process you are running is actually flushing its output buffers frequently.
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