how to start flask application code example

Example 1: simple flask app

# Extremely simple flask application, will display 'Hello World!' on the screen when you run it
# Access it by running it, then going to whatever port its running on (It'll say which port it's running on).
from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello, World!'

if __name__ == '__main__':
    app.run()

Example 2: flask how to run app

$ export FLASK_APP=hello.py
$ python -m flask run
 * Running on http://127.0.0.1:5000/

Example 3: basic flask app python

#Import Flask, if not then install and import.

import os
try:
  from flask import *
except:
  os.system("pip3 install flask")
  from flask import *

app = Flask(__name__)

@app.route("/")
def index():
  return "<h1>Hello World</h1>"

if __name__ == "__main__":
  app.run(host="0.0.0.0", port=8080, debug=False)