Importing from PWD using python -m fails in development environment

[jwg4]

Expected Behavior

We have a Flask app defined in a file which sits inside a folder, say app/run.py:

from flask import Flask

from foo import bar

app = Flask(__name__)

app.run()

The file imports from the top-level directory, in this case foo.py

bar = "SOMETHING TO IMPORT"

The empty file __init__.py exists in the directory app.

Using the default environment (production), we can run the Flask app by invoking the module from the top-level directory, using -m

python -m app.run

The foo module is imported correctly and the app runs.

 * Serving Flask app "run" (lazy loading)
 * Environment: production
   WARNING: Do not use the development server in a production environment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

Actual Behavior

If we try to use the development environment, setting the FLASK_ENV variable, it fails.

FLASK_ENV=development python -m app.run

 * Serving Flask app "run" (lazy loading)
 * Environment: development
 * Debug mode: on
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
 * Restarting with stat
Traceback (most recent call last):
  File "/home/jack/z/flask_dev/app/run.py", line 3, in <module>
    from foo import bar
ImportError: No module named foo

Environment

• Python version:
  Python 2.7.12 (default, Nov 20 2017, 18:23:56)
  [GCC 5.4.0 20160609] on linux2

• package versions:
  click==6.7
  Flask==1.0.2
  itsdangerous==0.24
  Jinja2==2.10
  MarkupSafe==1.0
  Werkzeug==0.14.1

[lepture]

Close it since it is not a bug of Flask.

It seems a misunderstanding of Python PATH. I don't know where you put your foo.py according to your description. It is better to ask your question on StackOverflow with a minimal example.

[jwg4]

With all due respect, it seems like you haven't understood the issue.

I do understand how PATH works, and I did say where foo.py is located.

I also said that starting the Flask server this way works for the production environment, but not for the development environment. So clearly, this is related to Flask rather than be a general issue of Python imports. But to be absolutely clear, if you don't have the call to app.run() in the file run.py, running a script in this way works perfectly well, with the module being imported correctly.

I would be grateful if you could look at this issue again and try to fully understand what is reported about the behavior of the Flask development server.

[lepture]

The file imports from the top-level directory, in this case foo.py

I'm sorry, but I don't fully understand your top-level. Is it /home/jack/z/flask_dev/app/foo.py or /home/jack/z/flask_dev/foo.py? I can only guess.

[lepture]

It is a werkzeug reloader issue.

Maybe related to pallets/werkzeug#461

[jwg4]

Thanks! Trying to understand exactly what that issue and #1246 imply for this.