App Engine Hello World Explained

Flask

Flask is a micro web framework written in Python.

Backend framework plays a crucial role in building robust and efficient web

applications. 

from flask import Flask 

app = Flask(__name__)

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

def hello():

    """Return a friendly HTTP greeting."""

    return 'Hello UCONN from John Iacovacci!\n'

if __name__ == '__main__':

    app.run(host='localhost', port=8080, debug=True)

# If `entrypoint` is not defined in app.yaml, App Engine

will look for an app

# Used when running locally only. When deploying to Google

App

# Engine, a webserver process such as Gunicorn will serve

the app. This

    # can be configured by adding an `entrypoint` to

app.yaml.

 

'__main__' is the name of the scope in which top-level code executes. 

 

A module’s __name__ is set equal to '__main__' when read from standard input, a script, or from an interactive prompt.

 

if __name__ == "__main__":

    # execute only if run as a script

    main()

 

__name__ is a built-in variable which evaluates to the name of the current module. T

Used to check whether the current script is being run on its own or being imported

somewhere else by combining it with if statement, as shown below.

Flask is a lightweight WSGI web application

framework. It is designed to make getting started quick and easy, with the ability to scale up

to complex applications. 

 A web framework (WF) or web application framework (WAF) is a software

framework that is designed to support the development of web applications

including web services, web resources, and web APIs.

Python code in one module gains access to the code in another module by the

process of importing it. 

The import statement is the most common way of invoking the import machinery.

Routing is the mechanism of mapping the URL directly to the code that creates

the webpage.

Use the route() decorator to bind a function to a URL.

app.route(rule, options)

• The rule parameter represents URL binding with the function.

• The options is a list of parameters to be forwarded to the underlying Rule object.

Http protocol is the foundation of data communication in world wide web. 

What is HTTP?

The Hypertext Transfer Protocol (HTTP) is designed to enable communications

between clients and servers.

HTTP works as a request-response protocol between a client and server.

Example: A client (browser) sends an HTTP request to the server; then the

server returns a response to the client. The response contains status information

about the request and may also contain the requested content.

HTTP Methods

• GET

• POST

• PUT

• HEAD

• DELETE

• PATCH

• OPTIONS

The two most common HTTP methods are: GET and POST.

The GET Method

GET is used to request data from a specified resource.

GET is one of the most common HTTP methods.

Note that the query string (name/value pairs) is sent in the URL of a GET request:

/test/demo_form.php?name1=value1&name2=value2

GET - Sends data in unencrypted form to the server. Most common method.

The POST Method

POST is used to send data to a server to create/update a resource.

The data sent to the server with POST is stored in the request body of the HTTP request:

POST /test/demo_form.php HTTP/1.1

POST is one of the most common HTTP methods.

Some other notes on POST requests:

• POST requests are never cached

• POST requests do not remain in the browser history

• POST requests cannot be bookmarked

• POST requests have no restrictions on data length

 POST - Used to send HTML form data to serve

By default, a route only answers to GET requests. You can use the

methods argument of the route() decorator to handle different HTTP methods.

Finally the run() method of Flask class runs the application on the local development

server.

app.run(host, port, debug, options)

localhost is a hostname that refers to the current computer used to access it. It is used to access

the network services that are running on the host via the loopback network interface.

Port 80 is HTTP. Port 443 is HTTPS. Port 8080 is a non-standard, high number port that is popular as an

alternative port for HTTP servers, most often application servers 

requirements.txt

requirements.txt file is used for specifying what python packages are required to run the project

you are looking at. 

 

app.yaml file. This configuration file defines your web app's settings for App Engine.

The app.yaml file also contains information about your app's code

$ gcloud app deploy

Deploy your app to upload and run it on App Engine. When you deploy your apps

, you create versions of those apps and their corresponding services in App Engine

 

Rendering Templates¶

render a template you can use the render_template() method. 

Provide the name of the template and the variables you want to pass to the template

engine as keyword arguments. 

 

 

The Request Context¶

The request context keeps track of the request-level data during a request.