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?
In python
session['username'] = 'username'
in jinja2 you can go
{{session['username']}}
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 %}
@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.