Constantly print Subprocess output while process is running

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()[0]
    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 @JF Sebastian 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="")

---

好吧，我设法解决它没有线程（任何建议，为什么使用线程会更好，赞赏）通过使用这个问题的代码片段在运行时拦截子进程的标准输出

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()[0]
    exitCode = process.returncode

    if (exitCode == 0):
        return output
    else:
        raise ProcessException(command, exitCode, output)

---

To print subprocess' output line-by-line as soon as its stdout buffer is flushed in Python 3:

from subprocess import Popen, PIPE, CalledProcessError

with Popen(cmd, stdout=PIPE, bufsize=1, universal_newlines=True) as p:
    for line in p.stdout:
        print(line, end='') # process line here

if p.returncode != 0:
    raise CalledProcessError(p.returncode, p.args)

Notice: you do not need p.poll() -- the loop ends when eof is reached. And you do not need iter(p.stdout.readline, '') -- the read-ahead bug is fixed in Python 3.

See also, Python: read streaming input from subprocess.communicate().

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