使用asyncio监视文件

Question

我正在尝试使用Python的asyncio库来确定一种观察文件外观的好方法.这是我到目前为止所提出的:

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

"""Watches for the appearance of a file."""

import argparse
import asyncio
import os.path


@asyncio.coroutine
def watch_for_file(file_path, interval=1):
    while True:
        if not os.path.exists(file_path):
            print("{} not found yet.".format(file_path))
            yield from asyncio.sleep(interval)
        else:
            print("{} found!".format(file_path))
            break


def make_cli_parser():
    cli_parser = argparse.ArgumentParser(description=__doc__)
    cli_parser.add_argument('file_path')
    return cli_parser


def main(argv=None):
    cli_parser = make_cli_parser()
    args = cli_parser.parse_args(argv)
    loop = asyncio.get_event_loop()
    loop.run_until_complete(watch_for_file(args.file_path))

if __name__ == '__main__':
    main()

我把它保存为watch_for_file.py,并可以运行它

python3 watch_for_file.py testfile

在另一个shell会话中,我发布

touch testfile

结束循环.

有没有比使用这个无限循环更优雅的解决方案yield from asyncio.sleep()？

Answer 1

嗯,有一些更好的,特定于平台的方式在创建文件时得到通知.Gerrat在他的评论中链接到一个用于Windows,并且pyinotify可以用于Linux.可能会插入那些特定于平台的方法asyncio,但是你最终会编写一大堆代码来使它以独立于平台的方式工作,这可能不值得只检查单个外观文件.如果你需要更复杂的文件系统观看,那么它可能值得追求.看起来pyinotify可以调整为添加其Notifier类的子类,插入asyncio事件循环(例如,已经有类tornado和asyncore).

对于你的简单用例,我认为你的轮询无限循环方法很好,但如果你需要,你也可以用事件循环来安排回调:

def watch_for_file(file_path, interval=1, loop=None):
    if not loop: loop = asyncio.get_event_loop()
    if not os.path.exists(file_path):
        print("{} not found yet.".format(file_path))
        loop.call_later(interval, watch_for_file, file_path, interval, loop)
    else:
        print("{} found!".format(file_path))
        loop.stop()

def main(argv=None):
    cli_parser = make_cli_parser()
    args = cli_parser.parse_args(argv)
    loop = asyncio.get_event_loop()
    loop.call_soon(watch_for_file, args.file_path)
    loop.run_forever()

不过,我不确定这比无限循环更优雅.

编辑:

只是为了好玩,我写了一个解决方案pyinotify:

import pyinotify
import asyncio
import argparse
import os.path


class AsyncioNotifier(pyinotify.Notifier):
    """

    Notifier subclass that plugs into the asyncio event loop.

    """
    def __init__(self, watch_manager, loop, callback=None,
                 default_proc_fun=None, read_freq=0, threshold=0, timeout=None):
        self.loop = loop
        self.handle_read_callback = callback
        pyinotify.Notifier.__init__(self, watch_manager, default_proc_fun, read_freq,
                                    threshold, timeout)
        loop.add_reader(self._fd, self.handle_read)

    def handle_read(self, *args, **kwargs):
        self.read_events()
        self.process_events()
        if self.handle_read_callback is not None:
            self.handle_read_callback(self)


class EventHandler(pyinotify.ProcessEvent):
    def my_init(self, file=None, loop=None):
        if not file:
            raise ValueError("file keyword argument must be provided")
        self.loop = loop if loop else asyncio.get_event_loop()
        self.filename = file

    def process_IN_CREATE(self, event):
        print("Creating:", event.pathname)
        if os.path.basename(event.pathname) == self.filename:
            print("Found it!")
            self.loop.stop()


def make_cli_parser():
    cli_parser = argparse.ArgumentParser(description=__doc__)
    cli_parser.add_argument('file_path')
    return cli_parser


def main(argv=None):
    cli_parser = make_cli_parser()
    args = cli_parser.parse_args(argv)
    loop = asyncio.get_event_loop()

    # set up pyinotify stuff
    wm = pyinotify.WatchManager()
    mask = pyinotify.IN_CREATE  # watched events
    dir_, filename = os.path.split(args.file_path)
    if not dir_:
        dir_ = "."
    wm.add_watch(dir_, mask)
    handler = EventHandler(file=filename, loop=loop)
    notifier = pyinotify.AsyncioNotifier(wm, loop, default_proc_fun=handler)

    loop.run_forever()

if __name__ == '__main__':
    main()