To launch programs from my Python-scripts, I'm using the following method:
def execute(command): process = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT) output = process.communicate() exitCode = process.returncode if (exitCode == 0): return output else: raise ProcessException(command, exitCode, output)
So when i launch a process like
Process.execute("mvn clean install"), my program waits until the the process is finished, and only then i get the complete output of my program. This is annoying if i'm running a process that takes a while to finish.
Can i let my program write the process output line by line, by polling the process output before it finishes in a loop or something?
**[EDIT] Sorry i didn't search very well before posting this question. Threading is actually the key. Found an example here which shows how to do it: ** Python Subprocess.Popen from a thread
You can use iter to process lines as soon as the command outputs them:
lines = iter(fd.readline, ""). Here's a full example showing a typical use case (thanks to @jfs for helping out):
from __future__ import print_function # Only Python 2.x import subprocess def execute(cmd): popen = subprocess.Popen(cmd, stdout=subprocess.PIPE, universal_newlines=True) for stdout_line in iter(popen.stdout.readline, ""): yield stdout_line popen.stdout.close() return_code = popen.wait() if return_code: raise subprocess.CalledProcessError(return_code, cmd) # Example for path in execute(["locate", "a"]): print(path, end="")
Ok i managed to solve it without threads (any suggestions why using threads would be better are appreciated) by using a snippet from this question Intercepting stdout of a subprocess while it is running
def execute(command): process = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT) # Poll process for new output until finished while True: nextline = process.stdout.readline() if nextline == '' and process.poll() is not None: break sys.stdout.write(nextline) sys.stdout.flush() output = process.communicate() exitCode = process.returncode if (exitCode == 0): return output else: raise ProcessException(command, exitCode, output)