Web2py Code Lab

Code Lab
+Colin Su
@littleq0903

Installing Python
http://python.org/downloads/
Python 2.7.x
Mac OS X & Linux - no installation needed, it's built-in

Hidden Documentation
help()
dir()

Types
str - String
list - List
tuple - Tuple
dict - Dictionary

String
encode(): Unicode -> Speciﬁc Encoding
decode(): Speciﬁc Encoding -> Unicode
Python uses Ascii & Unicode
>>> a = 'this is an ASCII string'
>>> b = u'This is a Unicode string'
>>> a = b.encode('utf8')

List
list is not array, is more like container
mutable container
>>> a = [1, 2, 3]
>>> print type(a)
<type 'list'>
>>> a.append(8)
>>> a.insert(2, 7)
>>> del a[0]
>>> print a
[2, 7, 3, 8]
>>> print len(a)
4

List - Iteration
List is iterable, you can loop over it
>>> a = [1, 2, 3]
>>> for i in a:
print i
1
2
3

Tuple
immutable version of List
>>> a = (1, 2, 3)
>>> print a[1]
2
>>> a[1] = 5
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment

Dictionary
store a mapping between a set of keys and a set of values
>>> d = {'user':'bozo', 'pswd':1234}
!

>>> d['user']
'bozo'
!

>>> d['pswd']
1234
!

>>> d['bozo']
!

Traceback (innermost last):
File '<interactive input>' line 1, in ?
KeyError: bozo

whlie
>>> i = 0
>>> while i < 10:
i = i + 1
>>> print i
10

if ... elif ... else
>>> for
>>>
>>>
>>>
>>>
>>>
>>>
zero
one
other

i in range(3):
if i == 0:
print 'zero'
elif i == 1:
print 'one'
else:
print 'other'

try ... except ... else ... ﬁnally
>>> try:
>>>
a = 1 / 0
>>> except Exception, e:
>>>
print 'oops: %s' % e
>>> else:
>>>
print 'no problem here'
>>> finally:
>>>
print 'done'
oops: integer division or modulo by zero
done

>>> try:
>>>
raise SyntaxError
>>> except ValueError:
>>>
print 'value error'
>>> except SyntaxError:
>>>
print 'syntax error'
syntax error

all statement for exception handling

exception can be vary

Functions
>>> def f(a, b):
return a + b
>>> print f(4, 2)
6

Functions - default value
>>> def f(a, b=2):
return a + b, a - b
>>> x, y = f(5)
>>> print x
7
>>> print y
3

Function Argument Packaging
arguments could be packaged into list or dictionary
* - position based arguments
** - name based arguments
>>> def f(*a, **b):
return a, b
>>> x, y = f(3, 'hello', c=4, test='world')
>>> print x
(3, 'hello')
>>> print y
{'c':4, 'test':'world'}

Function Argument Unpackaging
Vice versa, arguments could be extracted for functions

>>> def f(a, b):
return a + b
>>> c = (1, 2)
>>> print f(*c)
3

>>> def f(a, b):
return a + b
>>> c = {'a':1, 'b':2}
>>> print f(**c)
3

Lambda
anonymous function
Python features that function as ﬁrst-class object
>>> a = lambda b: b + 2
>>> print a(3)
5

Class
__init__ as constructor
>>> class MyClass(object):
>>>
z = 2
>>>
def __init__(self, a, b):
>>>
self.x = a
>>>
self.y = b
>>>
def add(self):
>>>
return self.x + self.y + self.z
>>> myinstance = MyClass(3, 4)
>>> print myinstance.add()
9

Class - Special Attributes, Methods, Operators
__len__ for len()
__getitem__ for indexing retrieve
__setitem__ for indexing setting

>>>
>>>
>>>
>>>
>>>
>>>
>>>
4
>>>
>>>
[3,

class MyList(object):
def __init__(self, *a): self.a = list(a)
def __len__(self): return len(self.a)
def __getitem__(self, i): return self.a[i]
def __setitem__(self, i, j): self.a[i] = j
b = MyList(3, 4, 5)
print b[1]
b.a[1] = 7
print b.a
7, 5]

import
import which, use which
>>> import random
>>> print random.randint(0, 9)
!
5

import all
>>> from random import *
>>> print randint(0, 9)

!

import renaming
>>> import random as myrand
>>> print myrand.randint(0, 9)

Datetime
library for dealing with time-related operation
>>> import datetime
>>> print datetime.datetime.today()
2008-07-04 14:03:90
>>> print datetime.date.today()
2008-07-04

Download web2py
http://www.web2py.com/init/default/download
Windows & Mac OS X - Packaged Executive
Linux - python web2py.py

Admin Panel
Choose admin password every time
Start server
Keep it open

Your First web2py Website
Application
Administrative interface

Administrative Interface
Installed Application Management
Install & Create New Application
Deployment
Debug
Code Editing

Pre-installed Applications
admin - the one you're using right now
examples - documentation and a replica of oﬃcial website
welcome - referred as the skeleton of applications

Let's Create a New Application
"New simple application" -> Create

Components In a Application
Models: the data representation
Controllers: application logic and workflow
Views: the data presentation, the interface to users
Languages: i18n, internalization
Modules: Python modules belongs to this application
Static files: image files, CSS files, JavaScript files...
Plugins: extensions of applications

URL Mapping
http://localhost:8000/<application>/<controller>/<handler>
Example
http://localhost:8000/mywebsite/default/index

Application
"mywebsite"

Controller
"default.py"

Handler
"def index(): ..."

Templates
Python Dictionary
!

{
}

"first_name": "Colin",
"last_name" : "Su"

HTML Template
<!DOCTYPE html>
<html>
<head>
<title>Hello Title</title>
</head>
<body>
<h1>Hello, I'm {{=first_name }} {{=last_name }}</h1>
</body>
</html>

Rendered HTML
<!DOCTYPE html>
<html>
<head>
<title>Hello Title</title>
</head>
<body>
<h1>Hello, I'm Colin Su</h1>
</body>
</html>

Default Template
controllers/default.py -> index() <=> views/default/index.html
You can change it by response.view = 'default/something.html'

Code Lab 0: Make Your Own Controller
Create codelab_ﬁrst.py in Controllers
Create codelab_ﬁrst/index.html in Views
GO EDITING!

Return a Dictionary
Try to return a customized dictionary
Click "exposes: index"

codelab_ﬁrst.py
!

def index():
my_dict = {
"message": "this is message",
"massage": "this is massage"
}
return my_dict

Now Template's Turn
Print your variables out by {{=var}}
codelab_ﬁrst/index.html
!

{{extend 'layout.html'}}
<h2>
{{=message}}
</h2>
<h3>
{{=massage}}
</h3>

Debugging a View
{{=BEAUTIFY(response._vars)}} to print out all variables
{{=response.toolbar()}} to enable a debug tool bar

Code Lab 1: Say My Name
codelab_saymyname.py in Controllers
codelab_saymyname/ask.html in Views
codelab_saymyname/say.html in Views

The Cleanest Controller Ever!
Directly return {} since we don't deal with it

codelab_saymyname.py
!

def ask():
return {}
!

def say():
return {}
!

Create a Form
"action" points to "say"
with a <input> named "visitor_name"

codelab_saymyname/ask.html
!

<h1>
What's Your Name?
</h1>
<form action="say">
<input name="visitor_name" />
<input type="submit" />
</form>
!

Let it go say
Get POST parameters by request.vars.var_name
codelab_saymyname/say.html
!

<h1>
Hello {{=request.vars.visitor_name}}
</h1>
!
!
!

web2py Libraries
are exposed to the handlers as global objects
Ex. request, response, BEAUTIFY...
source code ﬁles are in gluon folder
web2py/gluon

gluon/__init__.py
gluon/admin.py
gluon/cache.py
gluon/cfs.py
gluon/compileapp.py
gluon/contenttype.py
gluon/dal.py
gluon/decoder.py
gluon/fileutils.py
gluon/globals.py
!

gluon/highlight.py
gluon/restricted.py
gluon/html.py
gluon/rewrite.py
gluon/http.py
gluon/rocket.py
gluon/import_all.py gluon/sanitizer.py
gluon/languages.py
gluon/serializers.py
gluon/main.py
gluon/settings.py
gluon/myregex.py
gluon/shell.py
gluon/newcron.py
gluon/sql.py
gluon/portalocker.py gluon/sqlhtml.py
gluon/reserved_sql_keywords.py

gluon/streamer.py
gluon/template.py
gluon/storage.py
gluon/tools.py
gluon/utils.py
gluon/validators.py
gluon/widget.py
gluon/winservice.py
gluon/xmlrpc.py

web2py APIs - Global Objects
request - all conﬁguration in HTTP request
response - all conﬁguration in HTTP response
session
cache

request Object
extends Python dict class
basically a dictionary, but can be accessed as attributes 
request.vars or request['vars']
if an attribute does not exist, it returns None instead of an exception
read-only dictionary

Key Attributes in request Object
Dictionary-liked 

Boolean 

request.cookies 

request.is_local 

request.env 

request.is_https 

request.vars 

request.ajax

request.get_vars 
request.post_vars

Datetime 
request.now 

String 

request.utcnow

request.application 
request.controller 
request.function 
request.extension

(more...)

response Object
extends the same super class of request
it's a read-write dictionary (request is read-only)
usually aﬀects the browser behavior

Key Attributes in response Object
Dictionary-liked 

Functions 

response.cookies 

response.ﬂash() 

response.headers 

response.toolbar() 

response.meta 

response.write()

response._vars 
!

Strings 
response.title 
response.js 
response.delimiters [] 
response.view 
response.status 

(more...)

Session
also the Storage class (same of request, response)
the same user + the same time of login session

Operating Sessions
storing into session
Python

!

!

session.myvariable = "hello"
!

retrieving from session
Python
!

a = session.myvariable

Operating Sessions
Drops oﬀ all sessions
Python

!

!

session.forget(response)
!

Made sessions only be transferred under HTTPS protocol
Python
!

session.secure()

Caching
cache has two attributes: cache.ram, cache.disk
format: cache(<name>, <function>)

Caching in Memory
Python
!

def cache_in_ram():
import time
t = cache.ram('time', lambda: time.ctime(), time_expire=5)
return dict(time=t, link=A('click me', _href=request.url))

the output of lambda: time.ctime() is cached for 5 secs
'time' is used as the caching key

Responding
HTTP()
redirect()
URL()

HTTP()
It's an exception, need to be raised
determine the http responding status code  
e.g. 404, 500

HTTP(<status code>, <message>)
Python
!

def page_not_found():
raise HTTP(404, 'my message')

redirect()
redirect(<URL to redirect>)

Python
!

def index():
redirect("http://www.google.com")

URL()
generates internal URL path for actions or static ﬁles
all arguments will be parsed automatically
Python
!

URL('f')
>>> "/[application]/[controller]/f"
!

URL('f', args=['x', 'y'], vars=dict(z='t'))
>>> "/[application]/[controller]/f/x/y?z=t"

If you want to redirect to any application

Python
!

redirect(URL('f', args=['x', 'y'], vars=dict(z='t')))

HTML Helpers
generate any HTML tag in Python format
_ preﬁxed argument as html attribute
Template
!

{{=DIV('thisisatest', _id='123', _class='myclass')}}
!

-> <div id="123" class="myclass">thisisatest</div>

Template Basic Syntax
for ... in
while
def .... return

for ... in
{{pass}} as ending
Template

Rendered

!

!

{{items = ['a', 'b', 'c']}}
<ul>
{{for item in items:}}<li>{{=item}}</li>{{pass}}
</ul>

<ul>
<li>a</li>
<li>b</li>
<li>c</li>
</ul>
!

while
the condition expression needs to be given
Template

Rendered

!

!

{{k = 3}}
<ul>
{{while k > 0:}}<li>{{=k}}{{k = k - 1}}</
li>{{pass}}
</ul>

<ul>
<li>3</li>
<li>2</li>
<li>1</li>
</ul>
!


Template

Rendered

!

!

{{
import random
k = random.randint(0, 100)
}}
<h2>
{{=k}}
{{if k % 4 == 0:}}is divisible by 4
{{elif k % 2 == 0:}}is even
{{else:}}is odd
{{pass}}
</h2>

<h2>
64 is divisible by 4
</h2>
!
!


Template

Rendered

!

!

{{try:}}
Hello {{= 1 / 0}}
{{except:}}
division by zero
{{else:}}
no division by zero
{{finally}}
<br />
{{pass}}

Hello
division by zero
<br />
!

def ... return

Template

Rendered

!

!

{{def itemize(link):}}
<li><a href="http://{{=link}}">{{=link}}</a></li>
{{return}}
<ul>
{{itemize('www.google.com')}}
</ul>

<ul>
<li><a href="http:/www.google.com">www.google.com</
a></li>
</ul>

Abstraction Layer
In web2py, database operation has been abstracted into Python objects
No SQL needed, but the conception of SQL is still important
deﬁne your models in Models ﬁles

Connection
SQLite is ﬁle-based database which is widely used in development
scheme: sqlite://<filename>
Python
!

db = DAL('sqlite://storage.db')
!

Creating Tables
db.define_table(table_name, field1, field2 ... )

Python
!

db.define_table(
'purchase',
Field('buyer_id', db.person),
Field('product_id', db.product),
Field('quantity', 'integer'),
format = '%(quantity)s %(product_id)s -> %(buyer_id)s')
!

Query
conditions as query, connected with a "|"

Python
!

my_query = (db.mytable.myfield != None) | (db.mytable.myfield > 'A')
rows = db(my_query).select()
!

for row in rows:
print row.myfield
!
!

Insert
db.<table>.insert
db.<table>.bulk_insert

Python
!

>>> db.person.insert(name="Alex")
1
>>> db.person.insert(name="Bob")
2
!

>>> db.person.bulk_insert([{'name':'Alex'}, {'name':'John'}, {'name':'Tim'}])
[3,4,5]

Transaction
db.commit()
db.rollback()
rollback will ignore all operations since the last commit

Transaction Example
commit one more time to make changes to database
Python
!

db.commit()
try:
db.person.insert(name="bob")
except:
db.rollback()
else:
db.commit()
!

Practices
From the online web2py book
03 Overview
04 The core
05 The views
06 The database abstraction layer
07 Forms and validators

Resources
Quick Examples (Snippets) 
http://www.web2py.com/examples/default/examples
Online Book (free) 
http://web2py.com/books/default/chapter/29/00/preface
Python Cheat-sheet 
http://rgruet.free.fr/PQR26/PQR2.6_modern_a4.pdf

Open Source Project Contribution

Discussion is important
mailing list
documentation
IRC Channel
STFW & RTFM & GIYF

Git
version control system
coding history
distributed version control
Github
http://www.slideshare.net/littleq0903/introduction-to-git-10706480

Google Summer of Code
Sahana is the accepted organization again and again and again....
Google pays you if you spend your summer for coding
Idea Page
Idea -> Proposal -> get a mentor -> coding
https://developers.google.com/open-source/soc/

Thanks
Good luck to your development

Web2py Code Lab

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