Flask-Injector

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0.15.0 verified Mon Apr 27 auth: no python

Adds Injector, a Dependency Injection framework, support to Flask. Current version 0.15.0, maintained irregularly.

pip install flask-injector

Common errors

error ImportError: cannot import name 'FlaskInjector' from 'flask.ext.injector' ↓

cause The flask.ext namespace is deprecated and removed in Flask 2.3.

fix

Use 'from flask_injector import FlaskInjector' instead.

error TypeError: 'module' object is not callable when using @inject ↓

cause Importing @inject from flask_injector instead of injector.

fix

Import inject: from injector import inject

error AssertionError: No application found ↓

cause FlaskInjector not initialized or app object not passed correctly.

fix

Ensure FlaskInjector(app=app) is called after app creation and before first request.

Warnings

deprecated The 'flask.ext.injector' import pattern is deprecated and will break in Flask 2.3+. Use 'flask_injector' directly. ↓

fix Replace 'from flask.ext.injector import FlaskInjector' with 'from flask_injector import FlaskInjector'.

gotcha Injector uses static type hints for injection. If you omit type hints or use incorrect ones, injection may fail silently. ↓

fix Always annotate parameters with the exact class type expected, not strings or unions.

gotcha You must call FlaskInjector(app=app) before any request is handled. If called after route registration, dependencies may not be resolved inside views. ↓

fix Initialize FlaskInjector right after creating the Flask app and before returning it from the factory function.

breaking Injector 0.18+ changed the way modules are configured. If you use older patterns like 'modules=[lambda binder: binder.bind(...)]', this still works, but future versions may drop support. ↓

fix Use a function with a binder parameter, or a class implementing configure().

Imports

FlaskInjector

wrong

from flask.ext.injector import FlaskInjector

correct

from flask_injector import FlaskInjector

Flask extensions deprecated the flask.ext namespace in Flask 2.3.

request
wrong
```
from flask_injector import inject
```
correct
```
from injector import inject
```
The @inject decorator is from the injector library, not flask-injector.

Quickstart

Basic integration with Flask and Injector.

from flask import Flask, jsonify
from flask_injector import FlaskInjector
from injector import inject, singleton

class Greeter:
    def greet(self, name: str) -> str:
        return f'Hello, {name}!'

app = Flask(__name__)

@app.route('/')
@inject
def home(greeter: Greeter):
    return jsonify({'greeting': greeter.greet('World')})

def configure(binder):
    binder.bind(Greeter, to=Greeter, scope=singleton)

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

if __name__ == '__main__':
    app.run()