How do I watch a file for changes?

Solution 1:

Did you try using Watchdog?

Python API library and shell utilities to monitor file system events.

Directory monitoring made easy with

• A cross-platform API.
• A shell tool to run commands in response to directory changes.

Get started quickly with a simple example in Quickstart...

Solution 2:

If polling is good enough for you, I'd just watch if the "modified time" file stat changes. To read it:

os.stat(filename).st_mtime

(Also note that the Windows native change event solution does not work in all circumstances, e.g. on network drives.)

import os

class Monkey(object):
    def __init__(self):
        self._cached_stamp = 0
        self.filename = '/path/to/file'

    def ook(self):
        stamp = os.stat(self.filename).st_mtime
        if stamp != self._cached_stamp:
            self._cached_stamp = stamp
            # File has changed, so do something...

Solution 3:

Have you already looked at the documentation available on http://timgolden.me.uk/python/win32_how_do_i/watch_directory_for_changes.html? If you only need it to work under Windows the 2nd example seems to be exactly what you want (if you exchange the path of the directory with one of the files you want to watch).

Otherwise, polling will probably be the only really platform-independent option.

Note: I haven't tried any of these solutions.

Solution 4:

If you want a multiplatform solution, then check QFileSystemWatcher. Here an example code (not sanitized):

from PyQt4 import QtCore

@QtCore.pyqtSlot(str)
def directory_changed(path):
    print('Directory Changed!!!')

@QtCore.pyqtSlot(str)
def file_changed(path):
    print('File Changed!!!')

fs_watcher = QtCore.QFileSystemWatcher(['/path/to/files_1', '/path/to/files_2', '/path/to/files_3'])

fs_watcher.connect(fs_watcher, QtCore.SIGNAL('directoryChanged(QString)'), directory_changed)
fs_watcher.connect(fs_watcher, QtCore.SIGNAL('fileChanged(QString)'), file_changed)