pyinotify is a Python module for watching filesystems changes. By its design
pyinotify can be used for any kind of fs monitoring.

pyinotify relies on a recent Linux Kernel feature (merged in kernel 2.6.13)
called inotify. inotify is an event-driven notifier, its notifications are
exported from kernel space to user space. The raw interface of inotify is
compounded of three system calls. pyinotify binds these system calls and
provides an implementation on top of them offering a generic and abstract way
to use inotify with Python. Pyinotify doesn't requires much detailed knowledge
of inotify. Moreover, it only needs few statements for initializing, watching,
handling (eventually trough a new separate thread), and processing events
notifications through subclassing. The only things to know is the path of items
to watch, the kind of events to monitor and the actions to execute on these
notifications.

Note: pyinotify requires Python 2.3 and above, and Linux 2.6.13 at least.