Why do I get a 'NameError' with this import?

问题

I'm building a web app that uses Flask and SQLAlchemy, but I can't seem to see the reason why this won't import correctly and work.

I'm trying to test my database that I'm building, but I keep getting a NameError:

File1:

from flask.ext.sqlalchemy import SQLAlchemy
from flask import Flask
from File2 import db, data1, data2, data3

File2:

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///DB_File.db' # Uses '///' because '////' puts the file in '/' on server.
db.SQLAlchemy(app)

File2 is followed by some classes that inherit db.Model, but I don't think I need to include these in here.

To get the error, I'm pulling up a Python interpreter and doing import File1. This looks like:

>>> import File1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Tux/code/AppName/app/Util/File1.py", line 6, in <module>
    from KarmaCourtDB import db, data1, data2, data3
  File "/Tux/code/AppName/app/Util/File2.py", line 6, in <module>
    db.SQLAlchemy(app)
NameError: name 'db' is not defined

I'd really appreciate it if someone could help me out or point me in the right direction! This code was working before and I could create the database by using db.create_all() after importing it.

回答1:

db.SQLAlchemy(app) is not defining db, and is only attempting to run a SQLAlchemy() method on db. db = SQLAlchemy(app) however, would define db.

来源：https://stackoverflow.com/questions/27632513/why-do-i-get-a-nameerror-with-this-import