Flask AttributeError：模块对象没有属性“ app”

Question

我是Flask的新手，并且在flask_lab文件夹中flask run时，我下面导入了相关的AttributeError。

任何帮助将不胜感激。

工作目录：

flask_lab
├── __init__.py
├── Pipfile
├── Pipfile.lock
├── README.md
├── tmp
│   ├── __init__.py
│   └── test.py
└── app.py

flask_lab / app.py：

import os
import click

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

import flask_lab.tmp.test.demo

app = Flask(__name__)
prefix = 'sqlite:////'
app.config['SQLALCHEMY_DATABASE_URI'] = prefix + os.path.join(app.root_path, 'data.db')
db = SQLAlchemy(app)

class User(db.Model): 
    id = db.Column(db.Integer, primary_key=True) 
    name = db.Column(db.String(20))

flask_lab.tmp.test.demo()

flask_lab / tmp / test.py：

import flask_lab.app

print(flask_lab.app.db)


def demo():
    print('yeah!')

错误：

Traceback (most recent call last):
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/bin/flask", line 10, in <module>
    sys.exit(main())
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/flask/cli.py", line 894, in main
    cli.main(args=args, prog_name=name)
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/flask/cli.py", line 557, in main
    return super(FlaskGroup, self).main(*args, **kwargs)
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/click/decorators.py", line 64, in new_func
    return ctx.invoke(f, obj, *args, **kwargs)
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/flask/cli.py", line 767, in run_command
    app = DispatchingApp(info.load_app, use_eager_loading=eager_loading)
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/flask/cli.py", line 293, in __init__
    self._load_unlocked()
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/flask/cli.py", line 317, in _load_unlocked
    self._app = rv = self.loader()
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/flask/cli.py", line 377, in load_app
    raise_if_not_found=False)
  File "/home/huafeng/.local/share/virtualenvs/flask_lab-x_qc9OjH/lib/python3.6/site-packages/flask/cli.py", line 235, in locate_app
    __import__(module_name)
  File "/home/huafeng/Desktop/flask_lab/app.py", line 7, in <module>
    import flask_lab.tmp.test.demo
  File "/home/huafeng/Desktop/flask_lab/tmp/test.py", line 3, in <module>
    print(flask_lab.app.db)
AttributeError: module 'flask_lab' has no attribute 'app'

收到来自stackoverflow的抱怨，抱怨代码太多，细节不够。...更多的单词，更多的单词......

Answer 1

在解释app.py时，如果python解释器遇到行import flask_lab.tmp.test.demo，则它将立即开始解释tmp / test.py。但是tmp / test.py再次导入flask_lab。

这时，由于解释器已经遇到了flask_lab，它将开始在该命名空间中搜索app。但是它直到那条线才达到。由于您已经在模块中定义tmp.test之前导入了app，因此尚无flask_lab.app，因此会出现错误。

如果直接调用tmp.test，那么也会遇到循环导入错误。

因此，解决方法是避免循环导入。将db对象移动到一个单独的模块，并在这两个模块中调用它。 Flask-SQLAlchemy提供了一种称为init_app的方法，用于这种用例。

让我们创建一个名为common的模块，其中将包含公共变量。

flask_lab / common.py

from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()

flask_lab / app.py：

import os
import click

from flask import Flask
from .common import db
from .tmp.test import demo

class User(db.Model): 
    id = db.Column(db.Integer, primary_key=True) 
    name = db.Column(db.String(20))

app = Flask(__name__)
prefix = 'sqlite:////'
app.config['SQLALCHEMY_DATABASE_URI'] = prefix + os.path.join(app.root_path, 'data.db')
db.init_app(app)

demo()

flask_lab / tmp / test.py：

from .common import db

print(db)


def demo():
    print('yeah!')

请注意，我还用相对进口代替了flask_lab进口。他们更干净。包内的代码应避免在导入中使用包名。这样一来，如果您以后更改软件包名称，则无需更改其中的所有代码即可。