End of Adventures

After two price increases, and a horrendous, unexpected bill, and two weeks of hard work to escape from the walled gardens of App Engine, the Adventures are ended in the Cloud.

Installing PIL

Sooner or later you may need the PIL library for image manipulation. If you're using OS X, you will see it's not 100% obvious how to install - here is the solution.

For me, PYTHONPATH haven't worked, but this comment helped me out.

Also don't forget to restart AppEngine Launcher after PIL installed.

How to make a simple 404 page in App Engine

In app.yaml you have to define a 'catch all' mask at the very end of the file:

# --- 404 page ---

- url: /.*

script: 404.py

Of course you can use a static file as well.

Back-references are your friends

A very handy feature of database references is their automatic back-references pairs.

class User(db.Model):

name = db.StringProperty()

class Phone(db.Model):

number = db.PhoneNumberProperty()

user = db.ReferenceProperty(User)

# fetch one user

username = 'John'

user = User().all().filter('name = ', username).get()

# get the first associated phone number for a user

phonenum = user.phone_set[0].number

# list all phone numbers of the user

for phonenum in user.phone_set:

# phonenum here contains the user's actual phonenum in the list

The name of the back-reference property defaults to {model name}+'_set' in lower case, that's how 'phone_set' was made in the example. More about back-references can be read here.

Interactive Shell - a must have

Do you want to debug and see a memcache value on the live server? Or any other property? Deploy this interactive shell into your application's directory. Don't forget to set the rights to admin only in app.yaml.

Full Text Search

I thought it's impossible but then I've found an article about Full Text Searching in GAE - the nasty thing is, it's entirely undocumented. I'll give it a try soon. How-to can be found here.

Custom Django Filters in Google Application Engine

Here is a very good description how can you use custom Django filters in Google Application Engine.

I've modified a filter found on Django Snippets to convert ISO8859-2 / ISO8859-1 strings into URL friendly strings:

match_non_alnum = re.compile("[^a-zA-Z0-9]+")

def dig_url_encode(string):

"""Converts common ISO88592/1 chars to ASCII and removes any special chars"""

r = {

u'á': u'a',

u'é': u'e',

u'í': u'i',

u'ó': u'o',

u'ö': u'o',

u'õ': u'o',

u'ő': u'o',

u'ú': u'u',

u'ü': u'u',

u'ű': u'u',

u'û': u'u',

u'Á': u'A',

u'É': u'E',

u'Í': u'I',

u'Ó': u'O',

u'Ö': u'O',

u'Ő': u'O',

u'Ú': u'U',

u'Ü': u'U',

u'Ű': u'U'

}

for key, value in r.items():

string = string.replace(key, value)

return match_non_alnum.sub(' ', string).strip().replace(' ', '_')