by gorakhargosh

gorakhargosh / watchdog

Python library and shell utilities to monitor filesystem events.

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Python API and shell utilities to monitor file system events.

Works on Python 2.7 and 3.4+. If you want to use an old version of Python, you should stick with watchdog < 0.10.0.

Example API Usage

A simple program that uses watchdog to monitor directories specified as command-line arguments and logs events generated:

.. code-block:: python

import sys
import time
import logging
from watchdog.observers import Observer
from import LoggingEventHandler

if name == "main": logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(message)s', datefmt='%Y-%m-%d %H:%M:%S') path = sys.argv[1] if len(sys.argv) > 1 else '.' event_handler = LoggingEventHandler() observer = Observer() observer.schedule(event_handler, path, recursive=True) observer.start() try: while True: time.sleep(1) finally: observer.stop() observer.join()

Shell Utilities

Watchdog comes with an optional utility script called

. Please type
watchmedo --help
at the shell prompt to know more about this tool.

Here is how you can log the current directory recursively for events related only to

files while ignoring all directory events:

.. code-block:: bash

watchmedo log \
    --patterns="*.py;*.txt" \
    --ignore-directories \
    --recursive \

You can use the

subcommand to execute shell commands in response to events:

.. code-block:: bash

watchmedo shell-command \
    --patterns="*.py;*.txt" \
    --recursive \
    --command='echo "${watch_src_path}"' \

Please see the help information for these commands by typing:

.. code-block:: bash

watchmedo [command] --help


Tricks ~~~~~~~~~~~~~~~~~~~~~~~~~~
can read
files and execute tricks within them in response to file system events. Tricks are actually event handlers that subclass
and are written by plugin authors. Trick classes are augmented with a few additional features that regular event handlers don't need.

An example


.. code-block:: yaml

- watchdog.tricks.LoggerTrick:
    patterns: ["*.py", "*.js"]
- watchmedo_webtricks.GoogleClosureTrick:
    patterns: ['*.js']
    hash_names: true
    mappings_format: json                  # json|yaml|python
    mappings_module: app/javascript_mappings
    suffix: .min.js
    compilation_level: advanced            # simple|advanced
    source_directory: app/static/js/
    destination_directory: app/public/js/
      - app/static/js/vendor/jquery*.js
      - app/static/js/base.js
      - app/static/js/index-page.js
      - app/static/js/vendor/jquery*.js
      - app/static/js/base.js
      - app/static/js/about-page/**/*.js

The directory containing the

file will be monitored. Each trick class is initialized with its corresponding keys in the
file as arguments and events are fed to an instance of this class as they arrive.

Tricks will be included in the 0.5.0 release. I need community input about them. Please file enhancement requests at the

issue tracker


Install from PyPI using


.. code-block:: bash

$ python -m pip install watchdog

or to install the watchmedo utility:

$ python -m pip install watchdog[watchmedo]

Install from source:

.. code-block:: bash

$ python -m pip install -e .

or to install the watchmedo utility:

$ python -m pip install -e ".[watchmedo]"

Installation Caveats ~~~~~~~~~~~~~~~~~~~~ The

script depends on PyYAML_ which links with LibYAML, which brings a performance boost to the PyYAML parser. However, installing LibYAML is optional but recommended. On Mac OS X, you can use homebrew_ to install LibYAML:

.. code-block:: bash

$ brew install libyaml

On Linux, use your favorite package manager to install LibYAML. Here's how you do it on Ubuntu:

.. code-block:: bash

$ sudo aptitude install libyaml-dev

On Windows, please install PyYAML_ using the binaries they provide.


You can browse the latest release documentation_ online.


Fork the

_ on GitHub and send a pull request, or file an issue ticket at the
issue tracker
. For general help and questions use the official
mailing list
or ask on
_ with tag

Create and activate your virtual environment, then::

python -m pip install pytest pytest-cov
python -m pip install -e .[watchmedo]
python -m pytest tests

If you are making a substantial change, add an entry to the "Unreleased" section of the


Supported Platforms

  • Linux 2.6 (inotify)
  • Mac OS X (FSEvents, kqueue)
  • FreeBSD/BSD (kqueue)
  • Windows (ReadDirectoryChangesW with I/O completion ports; ReadDirectoryChangesW worker threads)
  • OS-independent (polling the disk for directory snapshots and comparing them periodically; slow and not recommended)

Note that when using watchdog with kqueue, you need the number of file descriptors allowed to be opened by programs running on your system to be increased to more than the number of files that you will be monitoring. The easiest way to do that is to edit your

file and add a line similar to::
ulimit -n 1024

This is an inherent problem with kqueue because it uses file descriptors to monitor files. That plus the enormous amount of bookkeeping that watchdog needs to do in order to monitor file descriptors just makes this a painful way to monitor files and directories. In essence, kqueue is not a very scalable way to monitor a deeply nested directory of files and directories with a large number of files.

About using watchdog with editors like Vim

Vim does not modify files unless directed to do so. It creates backup files and then swaps them in to replace the files you are editing on the disk. This means that if you use Vim to edit your files, the on-modified events for those files will not be triggered by watchdog. You may need to configure Vim appropriately to disable this feature.

About using watchdog with CIFS

When you want to watch changes in CIFS, you need to explicitly tell watchdog to use

, that is, instead of letting watchdog decide an appropriate observer like in the example above, do::
from watchdog.observers.polling import PollingObserver as Observer


  1. Python 2.7, 3.4 or above.
  2. pathtools_
  3. XCode_ (only on Mac OS X)
  4. PyYAML_ (only for
  5. argh_ (only for


Watchdog is licensed under the terms of the

Apache License, version 2.0

Copyright 2011

Yesudeep Mangalapilly

Copyright 2012 Google, Inc.


source code
_ is available at Github. Please report bugs and file enhancement requests at the
issue tracker

Why Watchdog?

Too many people tried to do the same thing and none did what I needed Python to do:

  • pnotify_
  • unison fsmonitor
  • fsmonitor_
  • guard_
  • pyinotify_
  • inotify-tools
  • jnotify_
  • treewalker_
  • file.monitor
  • pyfilesystem_

.. links: .. _Yesudeep Mangalapilly: [email protected] .. _source code: .. _issue tracker: .. _Apache License, version 2.0: .. _documentation: .. _stackoverflow: .. _mailing list: .. _repository: .. _issue tracker: .. _changelog:

.. _homebrew: .. _argh: .. _PyYAML: .. _XCode: .. _LibYAML: .. _pathtools:

.. _pnotify: .. _unison fsmonitor: .. _fsmonitor: .. _guard: .. _pyinotify: .. _inotify-tools: .. _jnotify: .. _treewalker: .. _file.monitor: .. _pyfilesystem:

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