[FIXED] UnboundLocalError: cannot access local variable 'Migrate' where it is not associated with a value - flask

Issue

I'm trying to set up Flask Migrate to handle my migrations for my app. I use a factory to handle my set-up and when I try to run flask db init I get the following error:

Traceback (most recent call last):
  File "/Users/grahammorby/Documents/GitHub/tagr-api/venv/bin/flask", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/Users/grahammorby/Documents/GitHub/tagr-api/venv/lib/python3.12/site-packages/flask/cli.py", line 1064, in main
    cli.main()
  File "/Users/grahammorby/Documents/GitHub/tagr-api/venv/lib/python3.12/site-packages/click/core.py", line 1078, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/Users/grahammorby/Documents/GitHub/tagr-api/venv/lib/python3.12/site-packages/click/core.py", line 1682, in invoke
    cmd_name, cmd, args = self.resolve_command(ctx, args)
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/grahammorby/Documents/GitHub/tagr-api/venv/lib/python3.12/site-packages/click/core.py", line 1729, in resolve_command
    cmd = self.get_command(ctx, cmd_name)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/grahammorby/Documents/GitHub/tagr-api/venv/lib/python3.12/site-packages/flask/cli.py", line 579, in get_command
    app = info.load_app()
          ^^^^^^^^^^^^^^^
  File "/Users/grahammorby/Documents/GitHub/tagr-api/venv/lib/python3.12/site-packages/flask/cli.py", line 313, in load_app
    app = locate_app(import_name, None, raise_if_not_found=False)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/grahammorby/Documents/GitHub/tagr-api/venv/lib/python3.12/site-packages/flask/cli.py", line 219, in locate_app
    __import__(module_name)
  File "/Users/grahammorby/Documents/GitHub/tagr-api/wsgi.py", line 3, in <module>
    app = init_app()
          ^^^^^^^^^^
  File "/Users/grahammorby/Documents/GitHub/tagr-api/application/__init__.py", line 26, in init_app
    Migrate = Migrate(app, db)
UnboundLocalError: cannot access local variable 'Migrate' where it is not associated with a value

and My set app application looks as follows:

from flask import Flask
from config import Config

from flask_sqlalchemy import SQLAlchemy
from flask_marshmallow import Marshmallow
from flask_bcrypt import Bcrypt
from flask_jwt_extended import JWTManager
from flask_migrate import Migrate


# Global accessible libraries
db = SQLAlchemy()
ma = Marshmallow()
bcrypt = Bcrypt()
JWTManager = JWTManager()

def init_app():
    app = Flask(__name__, instance_relative_config=False)
    app.config.from_object(Config)

    # Setup plugins
    db.init_app(app)
    ma.init_app(app)
    bcrypt.init_app(app)
    JWTManager.init_app(app)
    Migrate = Migrate(app, db)

    from models import User, App

    with app.app_context():
        # Blueprints
        from application.users import users_blueprint
        from application.apps import apps_blueprint

        app.register_blueprint(users_blueprint)
        app.register_blueprint(apps_blueprint)

        return app

I have tried to use it with init_app but that caused errors as well

Solution

You are getting an UnboundLocalError exception as you are using the same name for a function local variable and a module level variable in the line Migrate = Migrate(app, db) in your init_app function. Due to python variable scoping rule, the fact that you make an assignment to Migrate within the function means that a new local variable is created with that name and you lose access to the module level Migrate that you imported from flask_migrate. This can be solved by using a different name for the variable within the function.

Answered By - EAW