How do I run a python script whenever a file is created in a directory?

Solution 1:

Not a dupe, but in the accepted answer on this question, it is explained how to run a script (or any command) whenever a file is added or created in an arbitrary directory. In your case, the only needed event- trigger is:

-e create

Furthermore, since you are not using the path to the file as an argument, you can skip the --format -section.

The script to run in the background then simply is:

#!/bin/bash
DIR="/var/www/lager-scanner/filer/Nav/FromNav"
inotifywait -m -r -e create "$DIR" | while read f

do
    # you may want to release the monkey after the test :)
    echo monkey
    # <whatever_command_or_script_you_liketorun>
done

Explanation

As explained in the linked question:

-e create

will notice new files created inside the directory.

The options:

-m -r 

are to make the command run indefinitely ("monitor") and recursively in the directory.

According to this, using pyinotify is not the best option.

EDIT

In a comment you mention it does not work, and you mention the targeted folder is remote. Although not exactly the same, the issue seems related to this:
the change is not visible to the kernel; it happens entirely remotely.

A (tested) work around is to mount the remote folder locally.

Solution 2:

Here is a trimmed down version of the example from the inotify page on PyPI
(https://pypi.python.org/pypi/inotify) to get you started:

import inotify.adapters
import os

notifier = inotify.adapters.Inotify()
notifier.add_watch('/home/student')

for event in notifier.event_gen():
    if event is not None:
        # print event      # uncomment to see all events generated
        if 'IN_CREATE' in event[1]:
             print "file '{0}' created in '{1}'".format(event[3], event[2])
             os.system("your_python_script_here.py")

It creates a Inotify object then adds a directory to watch using the add_watch() method. Next it creates a event generator from the Inotify object using the event_gen() method. Finally it iterate overs that generator

Now file operations that affect the watched directory will generate one or more events. Each event takes the form of a tuple with four values:

• An _INOTIFY_EVENT tuple (omitted in the output below for clarity)
• A list of strings describing the events
• The name of the directory affected
• The name of the file affected

Running the above example with the first print statement uncommented and then creating the file 'new' in the watched directory gives this output:

( (...), ['IN_CREATE'], '/home/student', 'new')    
file 'new' created in '/home/student'
( (...), ['IN_ISDIR', 'IN_OPEN'], '/home/student', '')
( (...), ['IN_ISDIR', 'IN_CLOSE_NOWRITE'/home/student', '')
( (...), ['IN_OPEN'], '/home/student', 'new')
( (...), ['IN_ATTRIB'], '/home/student', 'new')
( (...), ['IN_CLOSE_WRITE'], '/home/student', 'new')

Since the 'IN_CREATE' event occurs when a new file is created, this is where you would add whatever code you wanted to run.