Blueprints

Blueprints are objects that can be used for sub-routing within an application. Instead of adding routes to the application instance, blueprints define similar methods for adding routes, which are then registered with the application in a flexible and pluggable manner.

Blueprints are especially useful for larger applications, where your application logic can be broken down into several groups or areas of responsibility.

My First Blueprint

The following shows a very simple blueprint that registers a handler-function at the root / of your application.

Suppose you save this file as my_blueprint.py, which can be imported into your main application later.

from sanic.response import json
from sanic import Blueprint

bp = Blueprint('my_blueprint')

@bp.route('/')
async def bp_root(request):
    return json({'my': 'blueprint'})

Registering blueprints

Blueprints must be registered with the application.

from sanic import Sanic
from my_blueprint import bp

app = Sanic(__name__)
app.blueprint(bp)

app.run(host='0.0.0.0', port=8000, debug=True)

This will add the blueprint to the application and register any routes defined by that blueprint. In this example, the registered routes in the app.router will look like:

[Route(handler=<function bp_root at 0x7f908382f9d8>, methods=None, pattern=re.compile('^/$'), parameters=[])]

Using blueprints

Blueprints have much the same functionality as an application instance.

Middleware

Using blueprints allows you to also register middleware globally.

@bp.middleware
async def halt_request(request):
	print("I am a spy")

@bp.middleware('request')
async def halt_request(request):
	return text('I halted the request')

@bp.middleware('response')
async def halt_response(request, response):
	return text('I halted the response')

Exceptions

Exceptions can be applied exclusively to blueprints globally.

@bp.exception(NotFound)
def ignore_404s(request, exception):
	return text("Yep, I totally found the page: {}".format(request.url))

Static files

Static files can be served globally, under the blueprint prefix.

bp.static('/folder/to/serve', '/web/path')

Start and stop

Blueprints can run functions during the start and stop process of the server. If running in multiprocessor mode (more than 1 worker), these are triggered after the workers fork.

Available events are:

before_server_start: Executed before the server begins to accept connections
after_server_start: Executed after the server begins to accept connections
before_server_stop: Executed before the server stops accepting connections
after_server_stop: Executed after the server is stopped and all requests are complete

bp = Blueprint('my_blueprint')

@bp.listener('before_server_start')
async def setup_connection(app, loop):
    global database
    database = mysql.connect(host='127.0.0.1'...)
    
@bp.listener('after_server_stop')
async def close_connection(app, loop):
    await database.close()

Use-case: API versioning

Blueprints can be very useful for API versioning, where one blueprint may point at /v1/<routes>, and another pointing at /v2/<routes>.

When a blueprint is initialised, it can take an optional url_prefix argument, which will be prepended to all routes defined on the blueprint. This feature can be used to implement our API versioning scheme.

# blueprints.py
from sanic.response import text
from sanic import Blueprint

blueprint_v1 = Blueprint('v1')
blueprint_v2 = Blueprint('v2')

@blueprint_v1.route('/')
async def api_v1_root(request):
    return text('Welcome to version 1 of our documentation')
    
@blueprint_v2.route('/')
async def api_v2_root(request):
    return text('Welcome to version 2 of our documentation')

When we register our blueprints on the app, the routes /v1 and /v2 will now point to the individual blueprints, which allows the creation of sub-sites for each API version.

# main.py
from sanic import Sanic
from blueprints import blueprint_v1, blueprint_v2

app = Sanic(__name__)
app.blueprint(blueprint_v1)
app.blueprint(blueprint_v2)

app.run(host='0.0.0.0', port=8000, debug=True)

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