Python：无法导入模块

Question

I am learning flask from https://blog.miguelgrinberg.com/

I have application microblog with filename as microblog.py

from app import app

and I have directory named app and it contains __init__.py with below code

from flask import Flask
from config import Config

app = Flask( __name__ )
app.config.from_object(Config)
from app import routes

But when I run flask run I am getting error as

ImportError: No module named 'app'

I understand like if I want to indicate a directory as a package then I have to include a __init__.py inside the directory and I did so for app directory.

Directory structure

.
├── __init__.py
├── app
│   ├── __init__.py
│   ├── forms.py
│   ├── routes.py
│   └── templates
│       ├── base.html
│       ├── index.html
│       └── login.html
├── config.py
└── microblog.py

Full stacktrace

flask run                                       
 * Serving Flask app "microblog.py"
 * Environment: production
   WARNING: Do not use the development server in a production environment.
   Use a production WSGI server instead.
 * Debug mode: off
Usage: flask run [OPTIONS]

Error: While importing "microblog.microblog", an ImportError was raised:

Traceback (most recent call last):
  File "~/anaconda3/envs/flask_python3.5.2/lib/python3.5/site-packages/flask/cli.py", line 235, in locate_app
    __import__(module_name)
  File "~/learning/migual_flask/microblog/microblog.py", line 1, in <module>
    from app import app
ImportError: No module named 'app'

And this code worked till recently and suddenly started giving troubles. I am unable to find where this is going wrong.

Any help greatly appreciated.

Thanks.

Answer 1

Okay, from what you post with the hierarchy, it's clear that it should work, but I suspect that you were importing from wrong directory.

Given the directory:

.
├── __init__.py
├── app
│   ├── __init__.py
│   ├── forms.py
│   ├── routes.py
│   └── templates
│       ├── base.html
│       ├── index.html
│       └── login.html
├── config.py
└── microblog.py

Assume you import them from root directory (the "." at the top):

$ls                                                                                                                                                        
__init__.py  app          config.py    microblog.py

$ls app
__init__.py  forms.py     routes.py

# which works
>>> import config
>>> import microblog
>>> import app

# and
>>> from app import routes
>>> from app import forms

I noticed that you have app = Flask() in your app/__init__.py , which is a very bad practice which should be avoided as much as possible (what makes you think it's good? I can't think of any), but it works for me:

>>> import app
>>> from app import app

# the first app is module
# the second is app = Flask()
# but the second one will overwrite the first one's name
# which is another terrible practice

And you can inspect a module:

>>> import app
>>> help(app) # app = Flask() is there