Presenter: James Huang Date: Sept. 29,

 HTTP and WWW  Bottle Web Framework  Request Routing  Sending Static Files  Handling HTML  HTTP Errors and Redirects  Cookies  Templates  Plugins  Demo 2

 World Wide Web (WWW) uses Hypertext Transfer Protocol (HTTP) as a standard for web client and web server to communicate.  HTTP uses a request-response computing model. ◦ A server listens for clients’ connection over TCP. ◦ A client (e.g. web browser) sends a request message to server. ◦ The server sends back a status line followed by a response message.  HTTP is a stateless protocol. ◦ Web applications often use cookies to maintain states. 3

 An HTTP client specifies request methods to distinguish different types of actions to be performed on the server.  GET ◦ Retrieves data from the server ◦ Should not have other effect on the server  POST ◦ Requests that the server accepts the data enclosed in the request ◦ Used to submit a form, upload a file, etc. 4

 An HTTP session is a sequence of request- response transactions. 5 GET /index.html HTTP/1.1 Host: HTTP/ OK Date: Mon, 29 Sep :50:21 GMT Server: WSGIServer/0.1 Python/2.7.2 Content-Length: 32 Content-Type: text/html; charset=UTF-8 Hello World Web Server Web Client

 Bottle is a web server that allows developers to write web applications in Python.  It is easy to install and use. ◦ Implemented in Python ◦ Has no dependency on any external libraries  Writing web application for Bottle is simple. ◦ A web application consists of callback functions that are called by Bottle to handle HTTP requests. ◦ Bottle handles errors and exceptions automatically. 6

7 # A simple web application from bottle import run, def home(): return ' Hello World. ‘ run(host='localhost', port=8080, debug=True) hello.py: Links ‘/’ to home() Starts web server on port 8080 Imports Bottle web framework

 URLs are linked to callback functions with route() decorator.  URL contains wildcards, dynamic route, can be used to match more than one ’) def hello(name): return greet(name)  More than one route can be used for a single ’) def hello(name=‘Stranger’): return greet(name) 8

 A simple wildcard (e.g. ) matches one or more characters up to the next slash (‘/’). ◦ E.g. ‘/hello/ ’ matches ‘/hello/bob’, but not ‘/hello’ or ‘/hello/john/smith’.  Each wildcard passes the matched part of URL as a keyword argument to the callback function.  Filters can be used to match specific wildcards and converts matched part of URL. ◦ :int – matches digits only and converts the value to integer ◦ :path – matches more than one path segment ◦ :re – matches with a regular expression 9

 A web application needs to have a callback to handle which files to serve to a client. ◦ Bottle does not automatically serve files to client.  Bottle provides static_file() helper function. 10 from bottle import ') def send_image(filename): return static_file(filename, root='/path/to/image/files', ') def server_static(filepath): return static_file(filepath, root='/path/to/your/html/files') match URL with regular expression match URL with path

 HTML usually specify to use POST request method to send form data.  Bottle’s route decorator applies to GET request method by default.  A web application can specify request method as an argument of route decorator. ◦ method=‘POST’)  Bottle also provides different decorators to handle different etc. as shortcuts.  The value of an Input field of a form can be retrieved with request object. 11

from bottle import get, post, request # or # def login(): return ''' Username: Password: # method='POST') def do_login(): username = request.forms.get('username') password = request.forms.get('password') if check_login(username, password): return " Your login information was correct. " else: return " Login failed. " 12 login() is called when user browse to /login do_login() is called when user submit the form request object is used to retrieve the value of an input field

 The abort() function is used to generate an HTTP error page. from bottle import route, def restricted(): abort(401, "Sorry, access denied.")  The redirect() function redirects a client to a different URL. from bottle import def wrong(): redirect("/right/url") 13

 A cookie stores site-specific text information in a web browser’s profile.  A web application creates a new cookie with Response.set_cookie(), access a cookie with Request.get_cookie(). def hello_again(): if request.get_cookie("visited"): return "Welcome back! Nice to see you again" else: response.set_cookie("visited", "yes") return "Hello there! Nice to meet you"

 A cookie can be controlled with different settings. ◦ max_age: maximum age in seconds ◦ expires: the timestamp when the cookie expires ◦ secure: limit the cookie to HTTPS connections  These settings can be specified as keyword arguments to Response.set_cookie().  Cookie expires at the end of a browser session, unless max_age or expires is set. 15

 Bottle provide a convenient way to generate web page from templates.  Here is an example template:  A web application uses templates with template() function. 16 %if name == 'World': Hello {{name}}! This is a test. %else: Hello {{name.title()}}! How are you? ') def hello(name): return template('hello_template', name=name) Python-like syntax hello_template.tpl

 Bottle supports third-party plugins: ◦ Bottle-Sqlite: SQLite3 database plugin ◦ Bottle-Redis: Redis database plugin ◦ Bottle-Flash: flash plugin 17 from bottle import route, install, template from bottle_sqlite import SQLitePlugin ') def show(db, post_id): c = db.execute('SELECT title, content FROM posts WHERE id = ?', (post_id,)) row = c.fetchone() return template('show_post', title=row['title'], text=row['content']) SQLitePlugin detects the use of db and creates a new database connection.

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