How to Create a Dash application that (re)actively reacts if contents of file changes

I read the article “Introducing Dash - Create Reactive Web Apps in pure Python”.

And I have a question about Dash:

I am trying to create a Dash application that (re)actively reacts if the contents of a file (.csv or .txt file) changes. If the contents of the files changes, the new contents should appear on screen in the Dash application.

How can this be done ?