How to view a file, not a directory for changes using Python?

Question

Question: How to view a file with changes using Python? suggests using watchdog, but I found that it could only see the directory, not the file, watchdog-test.py is a sample watchdog timer script:

$ python watchdog-test.py ab_test_res.sh & [1] 30628 fbt@fbt64 :~/laike9m$ Traceback (most recent call last): File "watchdog-test.py", line 15, in <module> observer.start() File "/usr/local/lib/python2.7/dist-packages/watchdog/observers/api.py", line 255, in start emitter.start() File "/usr/local/lib/python2.7/dist-packages/watchdog/utils/__init__.py", line 111, in start self.on_thread_start() File "/usr/local/lib/python2.7/dist-packages/watchdog/observers/inotify.py", line 121, in on_thread_start self._inotify = InotifyBuffer(path, self.watch.is_recursive) File "/usr/local/lib/python2.7/dist-packages/watchdog/observers/inotify_buffer.py", line 35, in __init__ self._inotify = Inotify(path, recursive) File "/usr/local/lib/python2.7/dist-packages/watchdog/observers/inotify_c.py", line 187, in __init__ self._add_dir_watch(path, recursive, event_mask) File "/usr/local/lib/python2.7/dist-packages/watchdog/observers/inotify_c.py", line 363, in _add_dir_watch raise OSError('Path is not a directory') OSError: Path is not a directory 

So what is the best solution? I am using Linux (Ubuntu 12.04). BTW I do not want to use a poll.

Answer 1

You can watch a file using a watchdog timer by looking at the directory in which the file is located and only respond to changes in events that affect your file. Something like this would do this for you:

 from watchdog.observers import Observer from watchdog.events import FileSystemEventHandler class FileModifiedHandler(FileSystemEventHandler): def __init__(self, path, file_name, callback): self.file_name = file_name self.callback = callback # set observer to watch for changes in the directory self.observer = Observer() self.observer.schedule(self, path, recursive=False) self.observer.start() self.observer.join() def on_modified(self, event): # only act on the change that we're looking for if not event.is_directory and event.src_path.endswith(self.file_name): self.observer.stop() # stop watching self.callback() # call callback from sys import argv, exit if __name__ == '__main__': if not len(argv) == 2: print("No file specified") exit(1) def callback(): print("FILE WAS MODIFED") FileModifiedHandler('.', argv[1], callback) 

I could only check this on windows, but it should be os agnostic.