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Templates

Starlette is not strictly coupled to any particular templating engine, but Jinja2 provides an excellent choice.

The Starlette application class provides a simple way to get jinja2 configured. This is probably what you want to use by default.

app = Starlette(debug=True, template_directory='templates')
app.mount('/static', StaticFiles(directory='statics'), name='static')


@app.route('/')
async def homepage(request):
    template = app.get_template('index.html')
    content = template.render(request=request)
    return HTMLResponse(content)

If you include request in the template context, then the url_for function will also be available within your template code.

The Jinja2 Environment instance is available as app.template_env.

Handling templates explicitly

If you don't want to use jinja2, or you don't want to rely on Starlette's default configuration you can configure a template renderer explicitly instead.

Here we're going to take a look at an example of how you can explicitly configure a Jinja2 environment together with Starlette.

from starlette.applications import Starlette
from starlette.staticfiles import StaticFiles
from starlette.responses import HTMLResponse


def setup_jinja2(template_dir):
    @jinja2.contextfunction
    def url_for(context, name, **path_params):
        request = context['request']
        return request.url_for(name, **path_params)

    loader = jinja2.FileSystemLoader(template_dir)
    env = jinja2.Environment(loader=loader, autoescape=True)
    env.globals['url_for'] = url_for
    return env


env = setup_jinja2('templates')
app = Starlette(debug=True)
app.mount('/static', StaticFiles(directory='statics'), name='static')


@app.route('/')
async def homepage(request):
    template = env.get_template('index.html')
    content = template.render(request=request)
    return HTMLResponse(content)

This gives you the equivalent of the default app.get_template(), but we've got all the configuration explicitly out in the open now.

The important parts to note from the above example are:

  • The StaticFiles app has been mounted with name='static', meaning we can use app.url_path_for('static', path=...) or request.url_for('static', path=...).
  • The Jinja2 environment has a global url_for included, which allows us to use url_for inside our templates. We always need to pass the incoming request instance in our context in order to be able to use the url_for function.

We can now link to static files from within our HTML templates. For example:

<link href="{{ url_for('static', path='/css/bootstrap.min.css') }}" rel="stylesheet">

Asynchronous template rendering

Jinja2 supports async template rendering, however as a general rule we'd recommend that you keep your templates free from logic that invokes database lookups, or other I/O operations.

Instead we'd recommend that you ensure that your views perform all I/O, for example, strictly evaluate any database queries within the view and include the final results in the context.