Migration from Flask

As Quart is compatible with the Flask public API it should be relatively straight forward to migrate to Quart from Flask. This migration basically consists of two steps, firstly replacing Flask imports with Quart imports and secondly inserting the relevant async and await keywords.

Import changes

Any import of a module from the flask package can be changed to be an import from the same module in the quart package. For example the following in Flask,

from flask import Flask, g, request
from flask.helpers import make_response

becomes in Quart,

from quart import Quart, g, request
from quart.helpers import make_response

noting that the imported objects have the same name in both packages except for the Quart and Flask classes themselves.

This can largely be automated via the use of find and replace.

Async and Await

As Quart is an asynchronous framework based on asyncio, it is necessary to explicitly add async and await keywords. The most notable place in which to do this is route functions, for example the following in Flask,

@app.route('/')
def route():
    data = request.get_json()
    return render_template_string("Hello {{name}}", name=data['name'])

becomes in Quart,

@app.route('/')
async def route():
    data = await request.get_json()
    return await render_template_string("Hello {{name}}", name=data['name'])

If you have sufficient test coverage it is possible to search for awaitables by searching for RuntimeWarning: coroutine 'XX' was never awaited.

The following common lines require awaiting, note that these must be awaited in functions/methods that are async. Awaiting in a non-async function/method is a syntax error.

await request.data
await request.get_json()
await request.form
await request.files
await render_template()
await render_template_string()

Testing

The test client also requires the usage of async and await keywords, mostly to await test requests i.e.

await test_client.get('/')
await test_client.post('/')
await test_client.open('/', 'PUT')

Extensions

To use a Flask extension with Quart see the Using Flask Extensions documentation.

Using Flask Extensions JSON Encoding