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importostar

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Introduction to Web development using Flask

You can learn web development with the Python programming language (Flask).

Flask is a python module that enables web development to be done in Python. A simple web application could be implemented with code.

If you are new to Flask, I recommend this book

Flask Hello World

The Flask module can be installed with pip. To use flask just import it in your Python app.

from flask import Flask

The program below creates the "Hello world" app in Python Flask

    from flask import Flask

    app = Flask(__name__)

    @app.route('/', methods=['GET'])
    def hello_world():
        return "Hello world\n"

    if __name__ == '__main__':
        app.run(host='0.0.0.0', port=5000)

You can see the following in the terminal, when running the above program,

    (venv) -bash-4.2$ python3 hello_world.py
     * Serving Flask app "hello_world" (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: off
     * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)

The "hello world function is added to '/' URL.

    @app.route('/', methods=['GET'])
    def hello_world():

The flask app starts with a run() call.

app.run(host='0.0.0.0', port=5000)

Use the app.run(debug = True) command to enable the debug option, the debugs option will be deactivated by default.

You can output anything like

python flask

You should use Python version 3 (or newer).

Routing

Routing is used to move directly from the URL to the correct Python function.

It is convenient to navigate the web sites without visiting the home page. The decorator app.route() is used for URL linking.

    @app.route('/python', methods=['GET']) # decorator
    def hello_python(): # bind to the method
        return "Hello Python\n"

Open the url localhost:5005/python, it shows the output of hello_python().

Redirect and errors

The redirect() method returns a reply object when called and
redirects it to another location with the HTTP status code.

It has this syntax:

 Flask.redirect(location, statuscode, response)

These are the regular HTTP status codes

  • HTTP_300_MULTIPLE_CHOICES
  • HTTP_301_MOVED_PERMANENTLY
  • HTTP_302_FOUND
  • HTTP_303_SEE_OTHER
  • HTTP_304_NOT_MODIFIED
  • HTTP_305_USE_PROXY
  • HTTP_306_RESERVED
  • HTTP_307_TEMPORARY_REDIRECT

The method abort() ends the session with an HTTP error.

Flask.abort(404)

You can use Flask to create all kinds of web apps, websites, to plot [1][2] and more.

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