Detect File Change Without Polling
Question:
I’m trying to use a method within a Python program to detect whether a file on the file system has been modified. I know that I could have something run on an every-5-seconds to check the last modification date off of the system, but I was curious as to whether there’s an easier method for doing this, without needing to require my program to check repeatedly.
Does anyone know of such a method?
Answers:
For linux, there is pyinotify.
From the homepage:
Pyinotify is a Python module for
monitoring filesystems changes.
Pyinotify relies on a 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 through three
system calls. pyinotify binds these
system calls and provides an
implementation on top of them offering
a generic and abstract way to
manipulate those functionalities.
Thus it is obviously not cross-platform and relies on a new enough kernel version. However, as far as I can see, requiring kernel support would be true about any non-polling mechanism.
You should also see inotifyx which is very similar to the previously mentioned pyinotify, but is said to have an API which changes less.
On windows there is:
watcher, which is a nice python port of the .NET FileSystemWatcher API.
Also there’s (the one I wrote) dirwatch.
Both rely on the windows ReadDirectoryChangesW function. Though for real work, I’d use watcher (proper C extension, good API, python 2 & 3 support).
Mine is mostly an experiment calling the relevant APIs on windows, so it’s only interesting if you want an example of calling these things from python.
Excellent cross platform library for watching directories.
From the website
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)
I’ve used it on a couple projects and it seems to work wonderfully.
I’m trying to use a method within a Python program to detect whether a file on the file system has been modified. I know that I could have something run on an every-5-seconds to check the last modification date off of the system, but I was curious as to whether there’s an easier method for doing this, without needing to require my program to check repeatedly.
Does anyone know of such a method?
For linux, there is pyinotify.
From the homepage:
Pyinotify is a Python module for
monitoring filesystems changes.
Pyinotify relies on a 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 through three
system calls. pyinotify binds these
system calls and provides an
implementation on top of them offering
a generic and abstract way to
manipulate those functionalities.
Thus it is obviously not cross-platform and relies on a new enough kernel version. However, as far as I can see, requiring kernel support would be true about any non-polling mechanism.
You should also see inotifyx which is very similar to the previously mentioned pyinotify, but is said to have an API which changes less.
On windows there is:
watcher, which is a nice python port of the .NET FileSystemWatcher API.
Also there’s (the one I wrote) dirwatch.
Both rely on the windows ReadDirectoryChangesW function. Though for real work, I’d use watcher (proper C extension, good API, python 2 & 3 support).
Mine is mostly an experiment calling the relevant APIs on windows, so it’s only interesting if you want an example of calling these things from python.
Excellent cross platform library for watching directories.
From the website
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)
I’ve used it on a couple projects and it seems to work wonderfully.