Auto reloading python Flask app upon code changes

问题:

I'm investigating how to develop a decent web app with Python. Since I don't want some high-order structures to get in my way, my choice fell on the lightweight Flask framework. Time will tell if this was the right choice.

So, now I've set up an Apache server with mod_wsgi, and my test site is running fine. However, I'd like to speed up the development routine by making the site automatically reload upon any changes in py or template files I make. I see that any changes in site's .wsgi file causes reloading (even without WSGIScriptReloading On in the apache config file), but I still have to prod it manually (ie, insert extra linebreak, save). Is there some way how to cause reload when I edit some of the app's py files? Or, I am expected to use IDE that refreshes the .wsgi file for me?

回答1:

The current recommended way (Flask >= 0.11) is with the flask command line utility.

http://flask.pocoo.org/docs/0.11/server/

Example:

$ export FLASK_APP=main.py
$ export FLASK_DEBUG=1
$ python -m flask run

or in one command:

$ FLASK_APP=main.py FLASK_DEBUG=1 python -m flask run

I prefer python -m flask run rather than flask run because the former also works with virtualenv.

If you want different port than the default (5000) add --port option.

Example:

$ python -m flask run --port 8080

More options are available with:

$ python -m flask run --help

回答2:

If you are talking about test/dev environments, then just use the debug option. It will auto-reload the flask app when a code change happens.

app.run(debug=True)

Or, from the shell:

$ export FLASK_DEBUG=1
$ flask run

http://flask.pocoo.org/docs/quickstart/#debug-mode

回答3:

In test/development environments

The werkzeug debugger already has an 'auto reload' function available that can be enabled by doing one of the following:

app.run(debug=True)

or

app.debug = True

You can also use a separate configuration file to manage all your setup if you need be. For example I use 'settings.py' with a 'DEBUG = True' option. Importing this file is easy too;

app.config.from_object('application.settings')

However this is not suitable for a production environment.

Production environment

Personally I chose Nginx + uWSGI over Apache + mod_wsgi for a few performance reasons but also the configuration options. The touch-reload option allows you to specify a file/folder that will cause the uWSGI application to reload your newly deployed flask app.

For example, your update script pulls your newest changes down and touches 'reload_me.txt' file. Your uWSGI ini script (which is kept up by Supervisord - obviously) has this line in it somewhere:

touch-reload = '/opt/virtual_environments/application/reload_me.txt'

I hope this helps!

回答4:

If you're running using uwsgi look at the python auto reload option:

uwsgi --py-autoreload 1

Example uwsgi-dev-example.ini:

[uwsgi]
socket = 127.0.0.1:5000
master = true
virtualenv = /Users/xxxx/.virtualenvs/sites_env
chdir = /Users/xxx/site_root
module = site_module:register_debug_server()
callable = app
uid = myuser
chmod-socket = 660
log-date = true
workers = 1
py-autoreload = 1

site_root/__init__.py

def register_debug_server():
    from werkzeug.debug import DebuggedApplication

    app = Flask(__name__)
    app.debug = True
    app = DebuggedApplication(app, evalex=True)
    return app

Then run:

uwsgi --ini uwsgi-dev-example.ini

Note: This example also enables the debugger.

I went this route to mimic production as close as possible with my nginx setup. Simply running the flask app with it's built in web server behind nginx it would result in a bad gateway error.

回答5:

A few updates for Flask 1.0

basic approach to hot re-loading is:

$ export FLASK_APP=my_application
$ export FLASK_ENV=development
$ flask run

• you should use FLASK_ENV=development (not FLASK_DEBUG=1)
• as a safety check, you can run flask run --debugger just to make sure it's turned on
• here is a working link to the docs (accepted answer's link is broken)

回答6:

To achieve this in PyCharm set 'Environment Variables' section to :

PYTHONUNBUFFERED=1;FLASK_DEBUG=1

For Flask 'run / debug configurations'