Watchdog

Python API and shell utilities to monitor file system events.

Example API Usage

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

import sys
import time
import logging
from watchdog.observers import Observer
from watchdog.events 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)
    except KeyboardInterrupt:
        observer.stop()
    observer.join()

Shell Utilities

Watchdog comes with a utility script called watchmedo. 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 *.py and *.txt files while ignoring all directory events:

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

You can use the shell-command subcommand to execute shell commands in response to events:

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

Please see the help information for these commands by typing:

watchmedo [command] --help

About `watchmedo` Tricks

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

An example tricks.yaml file:

tricks:
- 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/
    files:
      index-page:
      - app/static/js/vendor/jquery*.js
      - app/static/js/base.js
      - app/static/js/index-page.js
      about-page:
      - app/static/js/vendor/jquery*.js
      - app/static/js/base.js
      - app/static/js/about-page/**/*.js

The directory containing the tricks.yaml file will be monitored. Each trick class is initialized with its corresponding keys in the tricks.yaml 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.

Installation

Installing from PyPI using pip:

pip install watchdog

Installing from PyPI using easy_install:

easy_install watchdog

Installing from source:

python setup.py install

Installation Caveats

The watchmedo 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:

brew install libyaml

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

sudo aptitude install libyaml-dev

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

Documentation

You can browse the latest release documentation online.

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 ~/.profile 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 to appropriately to disable this feature.

Dependencies

Python 2.5 or above.
pathtools
select_backport (select.kqueue replacement for Python2.5/2.6 on BSD/Mac OS X)
XCode (only on Mac OS X)
PyYAML (only for watchmedo script)
argh (only for watchmedo script)

Licensing

Watchdog is licensed under the terms of the Apache License, version 2.0.

Project 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:

jvtm/watchdog