DAT310-server-p1

Web Programming Server-side programming I. Leander Jehl | University of
Stavanger

Recall from Last Time - HTTP requests - GET, POST
- HTTP responses

Today - Making a simple server-side application - Serve static
content (css ﬁles, html ﬁles, images, etc.) - Generate dynamic content - Handle input from URL and forms - Use templates

Flask - Framework for server-side web application development - Included
in the Anaconda distribution (i.e., no need to install anything) - Practical notes - Put each application in a separate folder (even if it consists of a single file) - This is also how the examples on GitHub are structured (examples/python/flask) - Don’t call your application flask (that would conflict with Flask itself) - http://flask.pocoo.org/ - Quickstart: http://flask.pocoo.org/docs/0.12/quickstart

from flask import Flask  app = Flask(__name__)    @app.route('/')  def
hello_world():  return("Hello, World!")    if __name__ == "__main__":  app.run() A Minimal Web Application  examples/python/ﬂask/0_minimal/app.py

from flask import Flask  app = Flask(__name__)    @app.route('/')  def
hello_world():  return "Hello, World!"    if __name__ == "__main__":  app.run() Create an instance of the Flask class (the argument is the name of the module) A Minimal Web Application  examples/python/ﬂask/0_minimal/app.py

from flask import Flask  app = Flask(__name__)    @app.route("/")  def
hello_world():  return "Hello, World!"    if __name__ == "__main__":  app.run() The app.route decorator tells Flask which URL should trigger this function A Minimal Web Application  examples/python/ﬂask/0_minimal/app.py

Exercise #0 https://github.com/uis-dat310-spring19/course-info/tree/master/  exercises/python/ﬂask1

- The route() decorator is used to bind a function
to a URL - Add variable parts to the URL by marking them as <varname> Routing  examples/python/ﬂask/1_routing/app.py @app.route("/")  def index():  return "Index Page"    @app.route("/info")  def hello():  return "This is a static info page"    @app.route("/user/<username>")  def user(username):  return "Showing the profile page for user {}".format(username)

Variable rules - <converter:varname> — optionally, a converter may be
used to convert the input variable to the speciﬁed format - Converters: - string (default) - int - ﬂoat - path (same as the default, but also accepts slashes) - …

@app.route("/package/<int:package_id>")  def package(package_id):  return "Showing the details for package #{}".format(package_id)
Example  examples/ﬂask/1_routing/app.py http://localhost:5000/package/abc http://localhost:5000/package/123

- url_for() — generates a URL for a speciﬁc function
- ﬁrst argument is the function name, optionally a number of additional arguments corresponding to the variable part of the URL rule URL Building  @app.route("/")  def index():  # ...    @app.route("/user/<username>")  def user(username):  # ... from flask import url_for print(url_for("index")) # /  print(url_for("user", username="JohnDoe")) # /user/JohnDoe

Serving Static Files - Dynamic web applications also need static
ﬁles (css, javascript, images, etc.) - Keep them under a folder called static - To generate URLs for them use the special static endpoint name url_for("static", filename="style.css")

HTML_FRAME_TOP = "<!DOCTYPE HTML>\n<html>\n<head>\n<title>My site</title>\n" \  "<link rel=\"stylesheet\" href=\"{css}\"/>\n</head>\n<body>\n"  HTML_FRAME_BOTTOM
= "</body>\n</html>\n"      @app.route("/")  def index():  html = HTML_FRAME_TOP.replace("{css}", url_for("static", filename="style.css"))  html += "<h1>Hello world</h1>"  html += HTML_FRAME_BOTTOM  return html Example  examples/ﬂask/2_static/app.py we replace the string {css} with the URL generated for the static "style.css" ﬁle

Accessing Request Data - In Flask, this information is provided
by the global request object from flask import request @app.route("/login", methods=["POST", "GET"])  def login():  error = None  if request.method == "POST":  if valid_login(request.form["username"],  request.form["password"]):  # do something  else:  error = "Invalid username/password"

Accessing Request Data - Accessing parameters submitted in the URL
- These are contained in request.args (dict) - Checking if a param has been provided - Getting param with default value - Iterating all parameters for k, v in request.args.items():  print("{:20} : {}".format(k, v)) if "name" in request.args:  print(request.args["name"]) print(request.args.get("name", ""))

Redirects and Errors - Redirect the user to another endpoint
- Abort a request with an early error code @app.route('/')  def index():  return redirect(url_for('login')) from flask import abort @app.route('/login')  def login():  abort(401)  # this_is_never_executed()

Custom Error Pages - Use the errorhandler() decorator from flask
import render_template  @app.errorhandler(404)  def page_not_found(error):  return render_template('page_not_found.html'), 404

from flask import Flask, url_for, redirect, request  @app.route("/")  def index(): 
return redirect(url_for("static", filename="form.html")) Example  examples/ﬂask/3_forms/app.py localhost:5000/static/form.html localhost:5000/ redirect to static form page from web root

Example  examples/ﬂask/3_forms/app.py localhost:5000/static/form.html http://localhost:5000/sendform @app.route("/sendform", methods=["POST"])  def sendform():  html =
HTML_FRAME_TOP.replace("{css}", url_for("static", filename="style.css"))  html += "Name: " + request.form["name"] \  + "<br />" \  + "Email: " + request.form["email"]  html += HTML_FRAME_BOTTOM  return html

DAT310-server-p1

DAT310-server-p1

Leander Jehl

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Web Programming Server-side programming I. Leander Jehl | University of

Recall from Last Time - HTTP requests - GET, POST

Today - Making a simple server-side application - Serve static

Flask - Framework for server-side web application development - Included

from flask import Flask  app = Flask(name)    @app.route('/')  def

from flask import Flask  app = Flask(name)    @app.route('/')  def

from flask import Flask  app = Flask(name)    @app.route("/")  def

Exercise #0 https://github.com/uis-dat310-spring19/course-info/tree/master/  exercises/python/ﬂask1

- The route() decorator is used to bind a function

Variable rules - <converter:varname> — optionally, a converter may be

@app.route("/package/<int:package_id>")  def package(package_id):  return "Showing the details for package #{}".format(package_id)

- url_for() — generates a URL for a speciﬁc function

Exercise #1 https://github.com/uis-dat310-spring19/course-info/tree/master/  exercises/python/ﬂask1

Serving Static Files - Dynamic web applications also need static

HTML_FRAME_TOP = "<!DOCTYPE HTML>\n<html>\n<head>\n<title>My site</title>\n" \  "<link rel=\"stylesheet\" href=\"{css}\"/>\n</head>\n<body>\n"  HTML_FRAME_BOTTOM

Accessing Request Data - In Flask, this information is provided

Accessing Request Data - Accessing parameters submitted in the URL

Redirects and Errors - Redirect the user to another endpoint

Custom Error Pages - Use the errorhandler() decorator from flask

from flask import Flask, url_for, redirect, request  @app.route("/")  def index():

Example  examples/ﬂask/3_forms/app.py localhost:5000/static/form.html http://localhost:5000/sendform @app.route("/sendform", methods=["POST"])  def sendform():  html =

Exercise #2 https://github.com/uis-dat310-spring19/course-info/tree/master/  exercises/python/ﬂask1