Python Web Tutorial

Rob Sanderson 
 ‐ azaroth42@gmail.com 
 ‐ @azaroth42 

Ed Summers 
 ‐ ehs@pobox.com 
 ‐ @edsu 

http://www.flickr.com/photos/42311564@N00/2355590274/

Dojo: Python for Web Interaction
Rob Sanderson, Ed Summers
Dev8D, Feb 24-27 2010, London

Overview

Python Dojo

•  Python Introduction

•  Web Programming Kata:
•  Find bands on Wikipedia
•  Find nationality of band
•  Find population of nation
•  Create chart of bands normalized by population


Python: Data Types

>>> ‘string’ “string” # strings are immutable
>>> u’unicode: xe4‘ # ä
>>> “””string that can have multiple lines”””

>>> 1 # int
>>> 1L # long int
>>> 1.0 # float

>>> [list, of, items] # mutable
>>> (tuple, of, items) # immutable

>>> {key : value, key2 : value2, …}

>>> None

>>> True, False # booleans


Python: Flow Control

>>> for x in iterable:
... # process x

>>> if test or test2 and not test3:
... # do something
... elif test4:
... # do something else
... else:
... # otherwise do this

>>> while test:
... # do something

>>> try:
... # try something
... except ExceptionType:
... # recover


Python: Classes, Functions

>>> def functionName(arg1, arg2=default):
... # do something

>>> class ClassName (ParentClass):
... property = value
...
... def __init__(self):
... # initialize
...
... def method(self, arg1, arg2=default):
... # do something

>>> what = ClassName()
>>> what.method(“arg1”, arg2=“arg2”)


Python: Other Important Stuff

>>> break

>>> continue

>>> raise Exception

>>> return value

>>> pass # no operation

>>> import module
>>> from module import something
>>> from module import * # import everything


Python Master Class: Basics

>>> ‘abcd’[0] = ‘z’ # error, as strings are immutable

>>> ‘’.join([list of strings]) # create string from list

>>> var = [x for x in iterable] # list comprehension

>>> a, b, c = (“a”, “b”, “c”) # scattered assignment

>>> var = a if test else b # ternary operator (test ? a : b)

>>> anonFn = lambda x: x+1 # anonFn(1)  2

>>> var = Function # var()  run Function
>>> var = Class # var()  new instance of Class


Python Master Class: Iterators

class Reverse:
"Iterator for looping over a sequence backwards"
def __init__(self, data):
self.data = data
self.index = len(data)
def __iter__(self):
return self
def next(self):
if self.index == 0:
raise StopIteration
self.index = self.index - 1
return self.data[self.index]

>>> for char in Reverse('spam'):
... print char
m
a
p
s


Python Master Class: Generators

def reverse(data):
for index in range(len(data)-1, -1, -1):
yield data[index]

>>> for char in reverse('golf'):
... print char
...
f
l
o
g


urllib

>>> import urllib
>>> urllib.quote('~azaroth/s?q=http://foo.com/')
'%7Eazaroth/s%3Fq%3Dhttp%3A//foo.com/'

>>> urllib.unquote('%7Eazaroth/s%3Fq%3Dhttp%3A//foo.com/')
'~azaroth/s?q=http://foo.com/'

>>> fh = urllib.urlopen('http://www.google.com/')
>>> html = fh.read()
>>> fh.close()

>>> fh.getcode()
200
>>> fh.headers.dict['content-type']
'text/html; charset=ISO-8859-1'


urllib2

>>> import urllib2
>>> ph = urllib2.ProxyHandler(

{'http' : 'http://proxyout.lanl.gov:8080/'})
>>> opener = urllib2.build_opener(ph)
>>> urllib2.install_opener(opener)
>>> # From now on, all requests will go through proxy

>>> r = urllib2.Request('http://www.google.com/')
>>> r.add_header('Referrer', 'http://www.somewhere.net')
>>> fh = urllib2.urlopen(r)
>>> html = fh.read()
>>> fh.close()

>>> # fh is the same as urllib's for headers/status

Rob Sanderson, Ed Summerrs

urlparse

>>> import urlparse
>>> pr = urlparse.urlparse(
'https://www.google.com/search?q=foo&bar=bz#frag')

>>> pr.scheme
'https'
>>> pr.hostname
'www.google.com'
>>> pr.path
'/search'
>>> pr.query
'q=foo&bar=bz'
>>> pr.fragment
'frag'


httplib

>>> import httplib
>>> cxn = httplib.HTTPConnection('www.google.com')
>>> hdrs = {'Accept' : 'application/rdf+xml'}
>>> path = "/search?q=some+search+query"

>>> cxn.request("HEAD", path, headers=hdrs)
>>> resp = cxn.getresponse()

>>> resp.status
200
>>> resp_hdrs = dict(resp.getheaders())
>>> resp_hdrs['content-type'] # :(
'text/html; charset=ISO-8859-1'

>>> data = resp.read()
>>> cxn.close()


lxml

$ easy_install lxml

>>> from lxml import etree
>>> et = etree.XML('<a b="B"> A <c>C</c> </a>')
>>> et.text
' A '
>>> et.attrib['b']
'B'
>>> for elem in et.iterchildren():
... print elem
<Element c at 16d1ed0>

>>> html = etree.parse(StringIO.StringIO("<html><p>hi"),
parser=etree.HTMLParser())
>>> html.xpath('/html/body/p')
[<Element p at 16e00f0>]


rdflib

$ easy_install rdflib

>>> import rdflib as rdf
>>> inp = rdf.URLInputSource(

'http://xmlns.com/foaf/spec/20100101.rdf')
>>> inp2 = rdf.StringInputSource("<a> <b> <c> .")
>>> graph = rdf.ConjunctiveGraph()
>>> graph.parse(inp)

>>> sparql = "SELECT ?l WHERE {?w rdfs:label ?l . }"
>>> res = graph.query(sparql, initNs={'rdfs':rdf.RDFS.RDFSNS}))
>>> res.selected[0]
rdf.Literal(u'Given name')

>>> nt = graph.serialize(format='nt')


json / simplejson

>>> try: import simplejson as json
... except ImportError: import json

>>> data = {'o' : (True, None, 1.0), "ints" : [1,2,3]}
>>> json.dumps(data)
'{"o": [true, null, 1.0], "ints": [1, 2, 3]}'

>>> json.dumps(data, separators=(',', ':')) # compact
'{"o":[true,null,1.0],"ints":[1,2,3]}'

>>> json.loads('[1,2,"foo",null]')
[1, 2, u'foo', None]


mod_python, mod_wsgi

import cgitb
from mod_python import apache
from mod_python.util import FieldStorage

def handler(req):
try:
form = FieldStorage(req) # dict-like object for query
path = req.uri
req.status = 200
req.content_type = "text/plain"
req.send_http_header()
req.write(path)
except:
req.content_type = "text/html"
cgitb.Hook(file=req).handle()
return apache.OK


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