Fix dash-asynchronous.py for dash 0.39.0

[ChrisArnault]

Hi

I have made asynchronous events work with dash 0.39.0 (where Event has been removed)
Here is the new code for dash-asynchronous.py
Note that this is tested under Winow10 thus I have used multithreaded setup (and single process)

[changes marked with trailing ###]

#################################################
import dash
from dash.dependencies import Input, Output ### removed Event from imports
import dash_core_components as dcc
import dash_html_components as html

import datetime
import time

class Semaphore:
def init(self, filename='semaphore.txt'):
self.filename = filename
with open(self.filename, 'w') as f:
f.write('done')

def lock(self):
    with open(self.filename, 'w') as f:
        f.write('working')

def unlock(self):
    with open(self.filename, 'w') as f:
        f.write('done')

def is_locked(self):
    return open(self.filename, 'r').read() == 'working'

semaphore = Semaphore()

def long_process():
if semaphore.is_locked():
raise Exception('Resource is locked')
semaphore.lock()
time.sleep(7)
semaphore.unlock()
return datetime.datetime.now()

app = dash.Dash()
server = app.server

def layout():
return html.Div([
html.Button('Run Process', id='button'),
dcc.Interval(id='interval', interval=500),
html.Div(id='lock'),
html.Div(id='output'),
])

app.layout = layout

@app.callback(
Output('lock', 'children'),
[Input('interval', 'n_intervals')]) ### New way to handle events for timers
def display_status(intervals):
return 'Running...' if semaphore.is_locked() else 'Free'

@app.callback(
Output('output', 'children'),
[Input('button', 'n_clicks')]) ### new way to handle events for buttons
def run_process(clicks):
return 'Finished at {}'.format(long_process()) if not clicks is None else '' ### no click at start

if name == 'main':
# app.run_server(debug=True, processes=5, threaded=False)
app.run_server(debug=True, processes=1, threaded=True) ### threaded mode (Windows10)

#################################################

here is my requirements.txt

#################################################
dash==0.39.0
dash-core-components==0.44.0
dash-html-components==0.14.0
dash-renderer==0.15.0
#################################################

Chris Arnault