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Adds Injector <https://github.com/alecthomas/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. You
can find Injector on PyPI <https://pypi.org/project/injector/> and Injector documentation on Read the Docs <https://injector.readthedocs.io/en/latest/>.
Flask-Injector is compatible with CPython 3.7+.
As of version 0.15.0 it requires Injector version 0.20.0 or greater and Flask
2.2.0 or greater.
GitHub project page: https://github.com/alecthomas/flask_injector
PyPI package page: https://pypi.org/project/Flask-Injector/
Changelog: https://github.com/alecthomas/flask_injector/blob/master/CHANGELOG.rst
Flask-Injector lets you inject dependencies into:
before_request handlersafter_request handlersteardown_request handlersapp.jinja_env.globals)Flask-Injector supports defining types using function annotations (Python 3), see below.
As Flask-Injector uses Injector under the hood you should find the
Injector documentation <https://injector.readthedocs.io/en/latest/>,
including the Injector API reference <https://injector.readthedocs.io/en/latest/api.html>,
helpful. The Injector README <https://github.com/alecthomas/injector/blob/master/README.md>_
provides a tutorial-level introduction to using Injector.
The Flask-Injector public API consists of the following:
FlaskInjector class with the constructor taking the following parameters:
app, an instance offlask.Flask [mandatory] – the Flask application to be usedmodules, an iterable of
Injector modules <https://injector.readthedocs.io/en/latest/api.html#injector.Binder.install>_ [optional]
– the Injector modules to be used.injector, an instance of
injector.Injector <https://injector.readthedocs.io/en/latest/api.html#injector.Injector>_ [optional]
– an instance of Injector to be used if, for some reason, it's not desirable
for FlaskInjector to create a new one. You're likely to not need to use this.request_scope_class, an injector.Scope <https://injector.readthedocs.io/en/latest/api.html#injector.Scope>_
subclass [optional] – the scope to be used instead of RequestScope. You're likely to need to use this
except for testing.RequestScope class – an injector.Scope <https://injector.readthedocs.io/en/latest/api.html#injector.Scope>_
subclass to be used for storing and reusing request-scoped dependenciesrequest object – to be used as a class decorator or in explicit
bind() <https://injector.readthedocs.io/en/latest/api.html#injector.Binder.bind>_ calls in
Injector modules.Creating an instance of FlaskInjector performs side-effectful configuration of the Flask
application passed to it. The following bindings are applied (if you want to modify them you
need to do it in one of the modules passed to the FlaskInjector constructor):
flask.Flask is bound to the Flask application in the (scope: singleton)flask.Config is bound to the configuration of the Flask applicationflask.Request is bound to the current Flask request object, equivalent to the thread-local
flask.request object (scope: request).. code:: python
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 (https://injector.readthedocs.io/en/latest/terminology.html#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.
Typically, Flask extensions are initialized at the global scope using a pattern similar to the following.
.. code:: python
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.
.. code:: python
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.