使用 python Popen 读取最后一行

Question

我有一个简单的python程序：

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。

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。 有没有办法在程序执行时读取输出中写入的最后一行？

Answer 1

sh.py 相当简单：

import sh

def process_line(line):
    print line

process = sh.python("test.py", _out=process_line)
process.wait()

Answer 2

您可以使用collections.deque 仅保存最后指定的行数：

#!/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()

见other tail-like solutions that print only the portion of the output

See here 如果您的子程序在非交互式运行时对其标准输出使用块缓冲（而不是行缓冲）。