flask.cli.NoAppException: Could not import “app”

from flask import Flask, render_template 
# Flask is a class that allows us to create an app
# render_template is a method offered by flask

app = Flask(__name__) # creates an app with the name of the file

@app.route('/') # route that listens to the homepage
def index(): # route handler
    # render_template(template_name_or_list) 
    # used to specify an html template to render to the user
    return render_template('index.html', data=[{
        'description': 'Todo 1'
    }, {
        'description': 'Todo 2'
    }, {
        'description': 'Todo 3'
    }])

# To run the app
# In the terminal
# FLASK_APP=app.py FLASK_DEBUG=true flask run

My application’s name is app.py, and it’s in a folder named ToDo-App, and within this folder there is another folder called templates, that contains the index.html file.

<html>
    <head>
        <title>Todo App</title>
    </head>
    <body>
        <ul>
            <!-- jinja for loop -->
            {% for d in data %}
            <li>{{ d.description }}</li>
            {% endfor %}
            <!--<li>Todo 1</li>
            <li>Todo 2</li>
            <li>Todo 3</li>
            <li>Todo 4</li>-->
        </ul>
    </body>
</html>

In the terminal:

Esam@DESKTOP-73QDAD3 MINGW32 /i/web/advanced-track/1-sql_and_data_modeling_for_the_web/ToDo-App
$ FLASK_APP=app.py FLASK_DEBUG=true flask run

Serving Flask app “app.py” (lazy loading)
Environment: production WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
Debug mode: on
Restarting with stat
Debugger is active!
Debugger PIN: 266-552-216
Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

When I opened this link http://127.0.0.1:5000/

Traceback (most recent call last): File “C:UsersEsamAppDataLocalProgramsPythonPython39-32Libsite-packagesflaskcli.py”, line 236, in locate_app import(module_name) ModuleNotFoundError: No module named ‘app’

During handling of the above exception, another exception occurred:

Traceback (most recent call last): File “C:UsersEsamAppDataLocalProgramsPythonPython39-32Libsite-packagesflaskcli.py”, line 337, in call rv = self._load_unlocked() File “C:UsersEsamAppDataLocalProgramsPythonPython39-32Libsite-packagesflaskcli.py”, line 324, in _load_unlocked self._app = rv = self.loader() File “C:UsersEsamAppDataLocalProgramsPythonPython39-32Libsite-packagesflaskcli.py”, line 381, in load_app app = locate_app(self, import_name, name) File “C:UsersEsamAppDataLocalProgramsPythonPython39-32Libsite-packagesflaskcli.py”, line 246, in locate_app raise NoAppException( flask.cli.NoAppException: Could not import “app”.

Answer

Depend on what machine your using, you need to do one of the following:

Unix Bash (Linux, Mac, etc.):

$ export FLASK_APP=hello
$ flask run

Windows CMD:

> set FLASK_APP=hello
> flask run

Windows PowerShell:

> $env:FLASK_APP = "hello"
> flask run

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Answer