‘set’ object is not reversible

use [] brackets in urls.py instead of {}

Here is what the above code is Doing:
1. We are creating a new URL pattern for our blog.
2. We are using the regex ^$ which matches an empty string. An empty string is what we get when we go to our site’s root URL.
3. We are telling Django that when we get an HTTP GET request to the root URL, we want to run the view called post_list.
4. We are giving the view post_list the name ‘post_list’ so we can refer to it easily in our template.