How to access session variables in jinja 2 - Flask

Question

Do I need to pass session variables manually from Flask to my HTML or are they automatically sent in some way?

Can I do

return render_template('index.html')

and access a session variable username, for example, like {{session['username'}} in the HTML file?

Solution 1

In python

session['username'] = 'username'

in jinja2 you can go

{{session['username']}}

Solution 2

If you want to isolate certain parts of your HTML using session you can call the session directly on those elements:

{% if session['username'] %}
<li>Logout</li>
{% endif %}

Solution 3

@bpb101 is correct on the Jinja2 format (though left out the spaces as others have mentioned). In the HTML/Jinja2 template you can simply call the session dictionary without passing it to the template:

{{ session['username'] }}

However the other example, in the Python code, would actually overwrite the value of session['username'] with the string 'username', due to variable assignment. If you were trying to set a variable to the value of session['username'] you would use:

username = session['username']

Otherwise if you just needed to test or use the value for some other reason you can access it directly for example:

if session['username'] == some_value:
    return "The username is", session['username']

Hopefully that helps for anyone new to Flask or Jinja2 that might wonder why their session variables are being overwritten.