Python Language Flask Jinja Templating


Similar to Meteor.js, Flask integrates well with front end templating services. Flask uses by default Jinja Templating. Templates allow small snippets of code to be used in the HTML file such as conditionals or loops.

When we render a template, any parameters beyond the template file name are passed into the HTML templating service. The following route will pass the username and joined date (from a function somewhere else) into the HTML.

def profile(username):
    joinedDate = get_joined_date(username) # This function's code is irrelevant
    awards = get_awards(username) # This function's code is irrelevant
    # The joinDate is a string and awards is an array of strings
    return render_template("profile.html", username=username, joinDate=joinDate, awards=awards)

When this template is rendered, it can use the variables passed to it from the render_template() function. Here are the contents of profile.html:

<!DOCTYPE html>
        # if username
            <title>Profile of {{ username }}</title>
        # else
            <title>No User Found</title>
        # endif
        {% if username %}
            <h1>{{ username }} joined on the date {{ date }}</h1>
            {% if len(awards) > 0 %}
                <h3>{{ username }} has the following awards:</h3>
                {% for award in awards %}
                {% endfor %}
            {% else %}
                <h3>{{ username }} has no awards</h3>
            {% endif %}
        {% else %}
            <h1>No user was found under that username</h1>
        {% endif %}
        {# This is a comment and doesn't affect the output #}

The following delimiters are used for different interpretations:

  • {% ... %} denotes a statement
  • {{ ... }} denotes an expression where a template is outputted
  • {# ... #} denotes a comment (not included in template output)
  • {# ... ## implies the rest of the line should be interpreted as a statement