# tree
├── calendar
│   ├── app.py
│   ├── calendar.py
│   ├── database.py
│   └── __init__.py
├── Pipfile
├── Pipfile.lock
├── README.md
└── tests
    └── __init__.py

# app.py
from flask import request, Flask, jsonify
from calendar.database import user, task, get_conn
from datetime import datetime

app = Flask(__name__)

# shell
(calendar) ~/P/P/W/calendar » export FLASK_APP=app.py
(calendar) ~/P/P/W/calendar » flask run
 * Serving Flask app "app.py"
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
Usage: flask run [OPTIONS]

Error: Could not import "app".