（十三）自动加载新模块

Python的第三方库watchdog可以利用操作系统的API来监控目录文件的变化，并发送通知。先用pip安装：

$ pip3 install watchdog

编写一个辅助程序pymonitor.py，让它启动app.py，并时刻监控www目录下的代码改动，有改动时，先把当前wsgiapp.py进程杀掉，再重启：

#!/usr/bin/env python3

import os, sys, time, subprocess
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler

def log(s):
    print('[Monitor] %s' % s)

class MyFileSystemEventHandler(FileSystemEventHandler):

    def __init__(self, fn):
        super(MyFileSystemEventHandler, self).__init__()
        self.restart = fn

    def on_any_event(self, event):
        if event.src_path.endswith('.py'):
            log('Python source file changed: %s' % event.src_path)
            self.restart()

command = ['echo', 'ok']    # 任意初始化两个字符串, 只是为了表明command一般由两段组成
process = None

def kill_process():
    global process
    if process:
        log('Kill process [%s]...' % process.pid)
        process.kill()
        process.wait()
        log('Process ended with code %s.' % process.returncode)
        process = None

def start_process():
    # global语句, 为定义在函数外的变量赋值, 或明确将要使用的变量是全局的而不是局部定义的
    global process, command
    log('Start process %s...' % ' '.join(command))
    process = subprocess.Popen(command, stdin=sys.stdin, stdout=sys.stdout, stderr=sys.stderr)

def restart_process():
    kill_process()
    start_process()

def start_watch(path, callback):
    # Observer类实现了监控文件变化触发对应事件的类, 然后调用关联的事件处理类来处理事件
    # 该类其实是threading.Thread的子类, 通过observer.start()使之运行在一个线程中, 不会阻塞主进程运行
    # 然后可以调用observer.stop()来停止该线程
    observer = Observer()
    # observer.schedule(event_handler,path,recursive=False)监控指定路径path
    # 该路径触发任何事件都会调用event_handler来处理, 如果path是目录, recursive=True则会递归监控该目录的所有变化
    # 当path变化时, 就会产生一个特定事件, 也就是event类的子类, 包含属性event_type,src_path,is_directory
    observer.schedule(MyFileSystemEventHandler(restart_process), path, recursive=True)
    observer.start()
    log('Watching directioy %s...' % path)
    start_process()
    try:
        while True:
            time.sleep(0.5)
    except KeyboardInterrupt:
        observer.stop()
    # 阻塞正在调用的线程，直到被调用join()方法的线程结束
    observer.join()

if __name__ == '__main__':
    argv = sys.argv[1:]    # 用法./pymonitor.py app.py
    if not argv:
        print('Usage: ./pymonitor your_script.py')
        exit(0)    # 正常退出
    if argv[0] != 'python3':
        argv.insert(0, 'python3')
    command = argv
    path = os.path.abspath('.')    # 当前目录
    start_watch(path, None)

给pymonitor.py加上可执行权限：

$ chmod u+x pymonitor.py

启动服务器：

$ ./pymonitor.py app.py

这里会报错不知道为什么：

/usr/bin/env: ‘python3\r’: No such file or directory

目测是window转到linux上\r的问题，但是怎们也消除不掉，先换另一种方法：

python3 pymonitor.py app.py

在编辑器中打开一个.py文件，修改后保存，看看命令行输出，是不是自动重启了服务器：

myweb@ubuntu:~/py3-webapp/www$ python3 pymonitor.py app.py
[Monitor] Watching directioy /home/myweb/py3-webapp/www...
[Monitor] Start process python3 app.py...
INFO:root:Found model: User (table: users)
...
INFO:root:Server started at http://192.168.179.140:7000...
# 我在这时修改了一个文件
[Monitor] Python source file changed: /home/myweb/py3-webapp/www/apis.py
[Monitor] Kill process [1308]...
[Monitor] Process ended with code -9.
[Monitor] Start process python3 app.py...
[Monitor] Python source file changed: /home/myweb/py3-webapp/www/apis.py
[Monitor] Kill process [1312]...
[Monitor] Process ended with code -9.
[Monitor] Start process python3 app.py...
[Monitor] Python source file changed: /home/myweb/py3-webapp/www/apis.py
[Monitor] Kill process [1313]...
[Monitor] Process ended with code -9.
[Monitor] Start process python3 app.py...
INFO:root:Found model: User (table: users)
...
INFO:root:Server started at http://192.168.179.140:7000...