Flask 应用程序出现“找不到 flask 应用程序。.....FLASK_APP 环境变量”错误 Flask 迁移

Question

I have a file db_table.py that looks like:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://root:password@localhost/mydb'

db = SQLAlchemy(app)
migrate = Migrate(app, db)
.....db tables....

When I try to run:

flask db init

I get:

Error: Could not locate Flask application. You did not provide the FLASK_APP environment variable.

I tried first manually setting FLASK_APP var, by doing set FLASK_APP=app.py then running flask db init again, but that didn't resolve the issue.

Answer 1

The flask command line argument needs to know what module to locate the current Flask app instance in.

Set FLASK_APP as an environment variable:

export FLASK_APP=db_table.py

before running your flask command-line app.

See the Command Line Interface documentation :

For the flask script to work, an application needs to be discovered. This is achieved by exporting the FLASK_APP environment variable. It can be either set to an import path or to a filename of a Python module that contains a Flask application.

You can also set the variable per command by setting it on the same command line:

FLASK_APP=db_table.py flask db init

Answer 2

You can refer to this documentation to learn how to set environment variables in Flask.

Unix Bash (Linux, Mac, etc.):

$ export FLASK_APP=hello
$ flask run

Windows CMD:

> set FLASK_APP=hello
> flask run

Windows PowerShell:

> $env:FLASK_APP = "hello"
> flask run

Answer 3

Some problem will can happen if you use DispatcherMiddleware (werkzeug.wsgi). Change return object from app_dispatch to app without app_dispatch for migrate time.

This is a rare case, I hope someone helps...

Answer 4

In VS code editor, click on Run and Debug. Select Flask debugger and type your file name. This worked for me and hope it works for you too.