* remember, we are using python 3; so either your commands use python3 or you have set up an alias as recommended in lab 5 http://gitlab.doc.gold.ac.uk/data-networks-web/lab-exercises/wikis/web-server
pip defaults to installing Python packages to a system directory (such as /usr/local/lib/python3.4). This requires root access. --user makes pip install packages in your home directory instead, which doesn't require any special privileges.
## set up a git repo
create a git repo called term-2-lab
## install flask
* pip install --user flask
note: pip defaults to installing Python packages to a system directory (such as /usr/local/lib/python3.4). This requires root access. --user makes pip install packages in your home directory instead, which doesn't require any special privileges.
* to list installed packages: _pip list_
## hello, world
make a directory lab-exercises
mkdir lab-exercises
cd lab-exercises
* create a hello world app.
* type it in by hand.
* read the explanation of the different lines [flask quickstart](http://flask.pocoo.org/docs/0.12/quickstart/#a-minimal-application)
## run using development server
add
if __name__ == '__main__':
app.run(debug=True,host='0.0.0.0',port=8000)
## port + ip
port 8000 is the port on which the virtual servers are available externally
1. it enables the debug mode on the Flask application.
## routing
* add a route that prints the time right now.
* you'll need to import the datetime module
* the date & time right now is given by datetime.datetime.now()
* but flask can only return a string so you also need _str_
* if you keep refreshing this view the time should keep updating
* => you can see that flask views are dynamic
## variable rules
* add a route with a variable so that /hello/bob will return "hello, bob!"
* see [variable rules](http://flask.pocoo.org/docs/0.12/quickstart/#variable-rules)
## rss feeds
* to make things a bit more interesting, we'll write an app that shows news headlines from rss feeds.
* we'll use this again later when we look at templates
* we'll need the feedparser module
so
pip install --user feedparser
##
here's the code
from flask import Flask
import feedparser
from random import randint
app = Flask(__name__)
BBC_FEED = "http://feeds.bbci.co.uk/news/rss.xml"
@app.route("/")
def headline():
feed = feedparser.parse(BBC_FEED)
article = feed['entries'][0]
return """<html>
<body>
<h1> BBC headline </h1>
<b>{0}</b> <br/>
<i>{1}</i> <br/>
<p>{2}</p> <br/>
</body>
</html>""".format(article.get("title"),
article.get("published"), article.get("summary"))
if __name__ == '__main__':
app.run(debug=True,host='0.0.0.0',port=8000)
* adapt the code to select a random headline from the first 10 in the rss feed
* you'll need the _randint_ function from the _random_ module
## module names
remember your simple app that showed the time.
what happens if you rename your app datetime.py then try to run it?
see also: the python standard library https://docs.python.org/3/library/index.html
## jinja templates
## templates
* we know we can return html from our flask view
* but it would be better to follow 'separation of concerns' by using a templating system.
* flask uses [jinja](http://jinja.pocoo.org/)
* there's a [quick intro on the flask site](http://flask.pocoo.org/docs/0.12/quickstart/#rendering-templates)
* jinja is a general templating system for python not just for flask
* there's fuller documentation at [Template Designer Documentation](http://jinja.pocoo.org/docs/2.10/templates/)
* it is used by Instagram, amongst others
## render_template
* to render a template you can use the render_template() method.
* flask will look for templates in the templates folder
* see http://flask.pocoo.org/docs/0.12/quickstart/#rendering-templates
## try it
* try creating a template for one of your mini-apps
* pass it a variable, which is rendered in the template as {{ variable }}
for example
@app.route('/hello/<name>')
def hello(name=None):
return render_template('hello.html', name=name)
## autoescaping
using jinja with flask helps tackle XSS because autoescaping is enabled for all templates ending in .html, .htm, .xml as well as .xhtml when using render_template()
## other variables
other variables which are available in jinja include
* config: The current configuration object (flask.config)
* request: The current request object (flask.request). This variable is unavailable if the template was rendered without an active request context.
* session: The current session object (flask.session). This variable is unavailable if the template was rendered without an active request context.
* get_flashed_messages(): The flask.get_flashed_messages() function.
we'll be covering these as part of flask over the next few weeks.
## jinja objects
all of the basic Python data structures, such as variables, objects, lists, and dictionaries, can be understood by
jinja and can be processed in a very similar way.
To output the result of a function in a template, just call the function as any regular Python function.
## loops
* jinja includes 'if' and 'for' loops.
the format of for loops is like this:
{% for article in articles %}
<b>{{article.title}}</b><br />
<p>{{article.summary}}</p>
{% endfor %}
## rss feeds
* create a template that loops over the news items from the bbc's rss feed
* you need to pass the articles to the template via render_template so it can loop over them
## 'if' statement
* in jinja, 'if' statements take the form
{% if <condition>}
<display something>
{% endif %}
* add an if statement to only display an rss feed if it contains a certain word
you can use
if <word> in article.summary
remember, words could have uppercase or lowercase letters. how do you make sure you only need to test for one case?
