Python Heroku app has 0 web dynos despite right Procfile and at right location
If you used a Procfile in deployment, make sure it does not have an extension such as .txt.  If it does, you might try:

Deleting that Procfile.txt.
Creating a new Procfile without the extension.
Pushing the new files to Heroku.
I deployed python app successfully but when I open the app it is showing me:
Application error
An error occurred in the application and your page could not be served. If you are the application owner, check your logs for details. You can do this from the Heroku CLI with the command
Heroku logs --tail
here is my heroku logs:

service= status=503 bytes= protocol=https
  2018-09-20T10:05:18.000000+00:00 app[api]: Build succeeded
  2018-09-20T10:19:34.769300+00:00 heroku[router]: at=error code=H14
  desc="No web processes running" method=GET path="/"
  host=demoaap.herokuapp.com request_id=1ae
  01895-963b-4211-9b30-d16de606c827 fwd="182.72.121.210" dyno= connect=
  service= s tatus=503 bytes= protocol=https

"heroku ps"commands gives:
No dynos on demoaap (demoaap is my app name)
moreover i have tried Herokuommand( " heroku ps:scale web=1" ) in order to run dynos but not working
.
Please help me out