Effective Python 读书笔记: 第36条: 用subprocess模块来管理子进程

# -*- encoding: utf-8 -*-

import os
import subprocess
from time import time

'''
第36条: 用subprocess模块来管理子进程

关键:
1 并发
含义: 轮流执行程序的方式

2 并行
含义: 同一时间执行多个程序

3 并发与并行的区别
并发速度要比并行要慢

4 运行子进程的方式
subprocess模块: 最简单的子进程管理模块,可管理输入流和输出流
特点: 子进程会独立于父进程运行
父进程: 是python的解释器
可以给communicate传入timeout参数，避免死锁

参考:
Effectiv Python 编写高质量Python代码的59个有效方法
'''

def useSubprocess():
    proc = subprocess.Popen(
        ['echo', 'I like python!'],
        stdout=subprocess.PIPE
    )
    out, err = proc.communicate()
    result = out.decode("utf-8")
    print result


def getSubprocessStatus():
    proc = subprocess.Popen(
        ['sleep', '0.3']
    )
    while proc.poll() is None:
        print "Working..."
    print "Exit status: {status}".format(
        status=proc.poll()
    )


def runSleep(period):
    proc = subprocess.Popen(
        ['sleep', str(period)]
    )
    return proc


def runMultipleSubprocess():
    start = time()
    processes = []
    for value in range(10):
        proc = runSleep(0.1)
        processes.append(proc)
    for proc in processes:
        proc.communicate()
    end = time()
    print "Cost {value} seconds".format(
        value=end - start
    )


def runOpenssl(data):
    env = os.environ.copy()
    # env['password'] = b'\xe24U\n\xdOQ135\x11'
    env['password'] = 'mypassword'
    proc = subprocess.Popen(
        ['openssl', 'enc', '-des3', '-pass', 'env:password'],
        env=env,
        stdin=subprocess.PIPE,
        stdout=subprocess.PIPE
    )
    proc.stdin.write(data)
    '''
    确保子进程获取输出
    '''
    proc.stdin.flush()
    return proc


def writeData():
    procs = []
    for value in range(3):
        data = os.urandom(10)
        proc = runOpenssl(data)
        procs.append(proc)
    for proc in procs:
        out, err = proc.communicate()
        print out[-10:]


def process():
    useSubprocess()
    getSubprocessStatus()
    runMultipleSubprocess()
    writeData()


if __name__ == "__main__":
    process()