使用 python Popen 读取最后一行 [英] Using python Popen to read the last line

问题描述

我有一个简单的python程序:

I have a simple python program:

test.py:

import time
for i in range(100000):
    print i
    time.sleep(0.5)

我想使用另一个执行上述程序的程序，以便在上述程序计数时读取最后一行输出.

I want to use another program that executes the above one in order to read the last line output while the above program is counting.

import subprocess

process = subprocess.Popen("test",stdout=PIPE)
sleep(20) # sleeps an arbitrary time
print stdout.readlines()[-1]

问题是 process.stdout.readlines() 一直等到 test.py 完成执行.有什么办法可以在程序执行时读取输出中写入的最后一行吗?

The problem is that process.stdout.readlines() waits until test.py finishes execution. Is there any way to read the last line that has been writen in the output while the program is executing?

推荐答案

您可以使用 collections.deque 只保存最后指定的行数:

You could use collections.deque to save only the last specified number of lines:

#!/usr/bin/env python
import collections
import subprocess
import time
import threading

def read_output(process, append):
    for line in iter(process.stdout.readline, ""):
        append(line)

def main():
    process = subprocess.Popen(["program"], stdout=subprocess.PIPE)
    # save last `number_of_lines` lines of the process output
    number_of_lines = 1
    q = collections.deque(maxlen=number_of_lines)
    t = threading.Thread(target=read_output, args=(process, q.append))
    t.daemon = True
    t.start()
    #
    time.sleep(20)

    # print saved lines
    print ''.join(q),
    # process is still running
    # uncomment if you don't want to wait for the process to complete
    ##process.terminate() # if it doesn't terminate; use process.kill()
    process.wait()

if __name__=="__main__":
    main()

请参阅其他仅打印输出部分的类似尾部的解决方案

如果您的子程序在运行时对其标准输出使用块缓冲(而不是行缓冲)，请参见此处非交互式.

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