Question

Ex，我需要在linux os上的某些目录中捕获删除和添加文件事件。我发现libs就像inotify和python包装器一样，但如果我想使用clear python代码，我应该每秒观察os.listdir(path)输出还是有一些方法可以完成这样的任务？

Answer 1

来源：http://code.activestate.com/recipes/215418-watching-a-directory-tree-on-unix/

watch_directories（）函数获取路径列表和可调用对象，然后重复遍历以这些路径为根的目录树，查看已删除的文件或更改其修改时间。然后，可调用对象将传递两个列表，其中包含已更改的文件和已删除的文件。

from __future__ import nested_scopes

import os, time

def watch_directories (paths, func, delay=1.0):
    """(paths:[str], func:callable, delay:float)
    Continuously monitors the paths and their subdirectories
    for changes.  If any files or directories are modified,
    the callable 'func' is called with a list of the modified paths of both
    files and directories.  'func' can return a Boolean value
    for rescanning; if it returns True, the directory tree will be
    rescanned without calling func() for any found changes.
    (This is so func() can write changes into the tree and prevent itself
    from being immediately called again.)
    """

    # Basic principle: all_files is a dictionary mapping paths to
    # modification times.  We repeatedly crawl through the directory
    # tree rooted at 'path', doing a stat() on each file and comparing
    # the modification time.  

    all_files = {}
    def f (unused, dirname, files):
        # Traversal function for directories
        for filename in files:
            path = os.path.join(dirname, filename)

            try:
                t = os.stat(path)
            except os.error:
                # If a file has been deleted between os.path.walk()
                # scanning the directory and now, we'll get an
                # os.error here.  Just ignore it -- we'll report
                # the deletion on the next pass through the main loop.
                continue

            mtime = remaining_files.get(path)
            if mtime is not None:
                # Record this file as having been seen
                del remaining_files[path]
                # File's mtime has been changed since we last looked at it.
                if t.st_mtime > mtime:
                    changed_list.append(path)
            else:
                # No recorded modification time, so it must be
                # a brand new file.
                changed_list.append(path)

            # Record current mtime of file.
            all_files[path] = t.st_mtime

    # Main loop
    rescan = False
    while True:
        changed_list = []
        remaining_files = all_files.copy()
        all_files = {}
        for path in paths:
            os.path.walk(path, f, None)
        removed_list = remaining_files.keys()
        if rescan:
            rescan = False
        elif changed_list or removed_list:
            rescan = func(changed_list, removed_list)

        time.sleep(delay)

if __name__ == '__main__':
    def f (changed_files, removed_files):
        print changed_files
        print 'Removed', removed_files

    watch_directories(['.'], f, 1)

如果您希望将某些作业发送到守护程序，但又不想使用某些IPC机制（如套接字或管道），则此配方非常有用。相反，守护程序可以坐下来查看提交目录，可以通过将文件或目录放入提交目录来提交作业。

不考虑锁定。 watch_directories（）函数本身并不需要做锁定;如果它错过了一次传球的修改，它会在下一次传球时注意到它。但是，如果将作业直接写入监视目录，则可调用对象可能会在作业文件仅写入一半时开始运行。要解决此问题，您可以使用lockfile; callable在运行时必须获取锁，并且提交者在希望添加新作业时必须获取锁。一种更简单的方法是依赖于原子的rename（）系统调用：将作业写入未被监视的临时目录，一旦文件完成，使用os.rename（）将其移动到提交目录中。

使用Python监视文件系统事件而不使用其他低级库

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