Flask-Injector

Adds Injector support to Flask, this way there's no need to use global Flask objects, which makes testing simpler.

Injector is a dependency-injection framework for Python, inspired by Guice.

Flask-Injector is compatible with CPython 3.3+. As of version 0.10.0 it requires Injector version 0.12.0 or greater and Flask 0.12.0 or greater.

GitHub project page: https://github.com/alecthomas/flask_injector

PyPI package page: https://pypi.python.org/pypi/Flask-Injector

Changelog: https://github.com/alecthomas/flask_injector/blob/master/CHANGELOG.rst

Features

Flask-Injector lets you inject dependencies into:

• views (functions and class-based)
• before_request handlers
• after_request handlers
• teardown_request handlers
• template context processors
• error handlers
• Jinja environment globals (functions in app.jinja_env.globals)
• Flask-RESTFul Resource constructors
• Flask-RestPlus Resource constructors

Flask-Injector supports defining types using function annotations (Python 3), see below.

Example application using Flask-Injector

import sqlite3
from flask import Flask, Config
from flask.views import View
from flask_injector import FlaskInjector
from injector import inject

app = Flask(__name__)

# Configure your application by attaching views, handlers, context processors etc.:

@app.route("/bar")
def bar():
    return render("bar.html")


# Route with injection
@app.route("/foo")
def foo(db: sqlite3.Connection):
    users = db.execute('SELECT * FROM users').all()
    return render("foo.html")


# Class-based view with injected constructor
class Waz(View):
    @inject
    def __init__(self, db: sqlite3.Connection):
        self.db = db

    def dispatch_request(self, key):
        users = self.db.execute('SELECT * FROM users WHERE name=?', (key,)).all()
        return 'waz'

app.add_url_rule('/waz/<key>', view_func=Waz.as_view('waz'))


# In the Injector world, all dependency configuration and initialization is
# performed in modules (http://packages.python.org/injector/#module). The
# same is true with Flask-Injector. You can see some examples of configuring
# Flask extensions through modules below.

# Accordingly, the next step is to create modules for any objects we want made
# available to the application. Note that in this example we also use the
# Injector to gain access to the `flask.Config`:

def configure(binder):
    binder.bind(
        sqlite3.Connection,
        to=sqlite3.Connection(':memory:'),
        scope=request,
    )

# Initialize Flask-Injector. This needs to be run *after* you attached all
# views, handlers, context processors and template globals.

FlaskInjector(app=app, modules=[configure])

# All that remains is to run the application

app.run()

See example.py for a more complete example, including Flask-SQLAlchemy and Flask-Cache integration.

Supporting Flask Extensions

Typically, Flask extensions are initialized at the global scope using a pattern similar to the following.

app = Flask(__name__)
ext = ExtClass(app)

@app.route(...)
def view():
    # Use ext object here...

As we don't have these globals with Flask-Injector we have to configure the extension the Injector way - through modules. Modules can either be subclasses of injector.Module or a callable taking an injector.Binder instance.

from injector import Module

class MyModule(Module):
    @provider
    @singleton
    def provide_ext(self, app: Flask) -> ExtClass:
        return ExtClass(app)

def main():
    app = Flask(__name__)
    app.config.update(
        EXT_CONFIG_VAR='some_value',
    )

    # attach your views etc. here

    FlaskInjector(app=app, modules=[MyModule])

    app.run()

Make sure to bind extension objects as singletons.