deprecate FLASK_ENV

[davidism]

Nothing in Flask ever ended up using FLASK_ENV/app.env specifically. It adds a layer of complexity to the already confusing ways that app.debug and app.testing can affect what happens internally. It's already possible to control debug mode, the debugger, and the reloader individually, there's no need for this extra switch.

Feedback from users on the Discord channel, and observation of questions on Stack Overflow, suggests this env var is a source of confusion or at least extra work.

FLASK_ENV=development is very verbose, and that isn't changing with the introduction of the --env development option. It's much shorter to use the --debug flag.

The original idea behind FLASK_ENV was that it would be used like NODE_ENV. Nothing ever came of it though. NODE_ENV as it's used with any frontend framework is a build-time flag, it has more meaning when it actually affects how JavaScript gets compiled, which is not something that maps to Python/Flask very well.

pallets/werkzeug#2480 will make the "don't use the dev server in production" warning always shown, instead of only in certain situations. With this there will be no current difference between FLASK_ENV=development and FLASK_DEBUG=1. It is also generally redundant given that the dev server should never be run in production, and FLASK_ENV is probably only given when running the dev server.

[GAEfan]

I must be missing something.

flask run --with-threads --host 127.0.0.1 --port 5000 --debug

yields

Error: No such option: --debug (Possible options: --debugger, --no-debugger)

[davidism]

--debug is an argument to flask, not to run. In Click, order matters, you can't mix options from one command with another.

flask --app example --debug run --port 8000

[crono782]

Seems like setting the DEBUG config key no longer works after this change.

from flask import Flask

app = Flask(__name__)
app.config['DEBUG'] = True

@app.route('/')
def index():
  return 'hello world'

results in:
$ flask run
WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.

• Debug mode: off
• Running on http://127.0.0.1:5000 (Press CTRL+C to quit)

[davidism]

Read the docs about the debug config. That is not related to this change.

[crono782]

Man, my bad. I tested same code on 2.13 and same result. For some reason I thought that was previously working. Disregard my gaff plz.