A reactive approach to monitor a file changes

file_changes.py

import rx
from rx import Observable
import os

def check_changes(previous, cur):
    current_modify_date = -1
    filename = previous['filename']

    if os.path.isfile(filename):
        current_modify_date = os.path.getmtime(filename)

    return {
        'previous_modify_date': current_modify_date,
        'changed': previous['previous_modify_date'] != current_modify_date,
        'filename': filename
    }

def file_changed_observable(file_name):
    return Observable.interval(100).scan(check_changes,
                                         seed={'previous_modify_date': -1,
                                               'changed': False,
                                               'filename': file_name}).filter(lambda val: val['changed'])

file_changed = file_changed_observable('test.txt')
file_changed.subscribe(print)