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Showing posts from May, 2010

list as default value in class __init__() - watchout for surprise

Note to self: don't use list as a default value in class methods if its going to be modified later, as it might cause some trouble.

Just realized something:

In [1]: class MyClass(object):
...: def __init__(self,data=[]):
...: = data
...: def addData(self,value):

In [2]: obj = MyClass()

In [3]: obj.addData('hello')

In [4]:
Out[4]: ['hello']

In [5]: obj2 = MyClass()

In [6]:
Out[6]: ['hello']

In [7]: obj3 = MyClass([])

In [8]:
Out[8]: []

In [12]: def myfunc(val,data=[]):
....: data.append(val)
....: return data

In [13]: myfunc(1)
Out[13]: [1]

In [14]: myfunc(2)
Out[14]: [1, 2]

In [15]: myfunc(3)
Out[15]: [1, 2, 3]

At first i thought its a bug/weirdness, but after banging my head a bit to wall and a long stare at the ceiling, it made sense.

During class definition, the list object already instantiated. Therefore, th…

Using deliverance as WSGI pipeline to elegantly theme a repoze.bfg project

I was looking around for template inheritance solution for repoze.bfg, as it seems like by default, BFG does not have context view traversal support to acquire template macros.

In Plone/Grok template inheritance can be done by registering main_template as a view, and using a template that fill the slots in main_template such as this:
<html xmlns:tal=""
<div metal:fill-slot="main">
Some content

However, by default, repoze.bfg does not support getting view macro from a context. So a PageTemplate object need to by passed by a view in order to use the macro from the template. Eg:
from repoze.bfg.chameleon_zpt import get_template

def my_view(context,request):
main_template = get_template('templates/main_t…

repoze.bfg - Introduction and bootstrapping it on buildout

2 months without a post here .. T_T ... must .. restart .. blogging ...

Anyway, I've been poking around with repoze.bfg since last week and growing to love it by the days. Been thinking to post a blog on getting started on it but was a bit lazy .. until I saw lowkster's post about bfg at a few days ago.

Full documentation at

A little review

I love Zope Component Architecture because the modularity/reusability it offers, but Bluebream, Grok and Zope2 feels a bit big for simple web apps or for introducing ZCA to new people. Then I saw BFG.

BFG simplifies many concepts which I'm familiar with in Zope2/Zope3, and it does it without overwhelming developers with other parts of the framework. Not endorsing any type of storage backend, and giving an option between URL routing and traversal or a mix of both is a plus.

The initial base code is simple and straightforward, and there are no need to subclass any parent class when you want to crea…