Set up env (virtual environment)

tutorial

$ python -m venv env  # Windows

$ python3 -m venv env  # Linux or macOS

In python, there is no central lib management tools like Maven in Java, and it is not possible to have different version of same lib, so we need to create a env to manage the lib we use in this project

now we created the env, we need to activate it

$ source env/bin/activate  # Linux or macOS

$ .\env\Scripts\activate  # Windows

if you successfully activated the env, you will see the env name in the terminal

(env) $

if you want to deactivate the env, just type deactivate in the terminal

Install Flask

$ pip install Flask

$ pip install flask==2.1.3 # install specific version

Create a simple Flask app

from flask import Flask

app = Flask(__name__)

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

save the code above to a file named app.py, and run the app

$ export FLASK_APP=app.py  # Linux or macOS
> $env:FLASK_APP = "hello.py"  # Windows

$ flask run