Skip to main content

An object system for building declarative configurations in Python.

Project description


An object system for building declarative configurations in Python.

A class that has rich(ish) keyword-parameter handling, including
[explicit handling of required parameters](,
[declaration of parameter dependencies]( and
[basic type-checking](

Keyword parameter processing will be performed for any method on the
`Deconfigurable` that is decorated with the `@parameter` decorator. Each of these
decorated methods performs the processing specific to that parameter. The
returned value is then assigned on the appropriately named attribute.

>>> @parameter('foo')
>>> def handle_foo(self, value):
... return value

Pass-Through Parameters:

If your parameter doesn't require any special treatment and should simply
be stored on the Deconfigurable a shorthand can be used. Simply decorate
a parameter method that passes, and `value` will be used as is.

>>> @parameter('foo')
>>> def handle_foo(self, value):
... pass

Required Parameters:

Parameters are required by default. This means that a `RequiredParameterError`
will be raised if the `Deconfigurable.__init__` doesn't recieve the designated
named argument.

Passing `default=` to `@parameter` will prevent the parameter from
raising `RequiredParameterError` if the parameter isn't provided a value.

>>> @parameter('foo', default='bar')
>>> def handle_foo(self, value):
... pass

Type-Checked Parameters:

A basic mechanism is supplied for ensuring that the passed parameter value
is of a specific type. By supplying a type value to the `@parameter`'s
`ensure_type` keyword arguement any value passed in will be validated with
an *isinstance check*.

>>> @parameter('bars', ensure_type=list)
>>> def handle_bars(self, value):
... pass

Dependency Parameters:

Sometimes we will want to defer processing of a parameter until some other
parameter has been processed first. To do so, simply pass a list of
dependencies, `depends_on`, to `@parameter`.

>>> @parameter('foo')
>>> def handle_foo(self, foo):
... pass

>>> @parameter('bar', depends_on=('foo', ))
>>> def handle_bar(self, bar):
... # offset bar by foo
... return bar +

Contrived Example:

class Person(Deconfigurable):
def format_name(cls, name):
return name.strip().lower().capitalize()

@parameter('first_name', ensure_type=str)
def handle_first(self, name):
return Person.format_name(name)

@parameter('last_name', ensure_type=str)
def handle_last(self, name):
return Person.format_name(name)

@parameter('age', ensure_type=int)
def handle_age(self, value): pass

@parameter('registered_to_vote', ensure_type=bool, depends_on=('age',))
def handle_vote(self, value):
if self.age < 18:
value = False
return value

>>> me = Person(
... first_name='Dustin',
... last_name='Lacewell',
... age=25, registered_to_vote=True,
... )
>>> print me.first_name, ' can vote: ', me.registered_to_vote
Dustin can vote: True

>>> kid = Person(
... first_name='Some Kid',
... last_name='Smith',
... age=12, registered_to_vote=True,
... )
>>> print kid.first_name, ' can vote: ', kid.registered_to_vote
SomeKid can vote: False

Example from Spidersilk (twisted.web config lib):

from twisted.web.static import File
from twisted.web.proxy import ReverseProxyResource

from spidersilk import Domain, Httpd

application = Httpd(
port = 80,
default = '',
domains = [
resource=ReverseProxyResource('localhost', 8088, ''),

Where Domain is implemented as:

class Domain(Deconfigurable):
@parameter('hostname', ensure_type=str)
def _arg_hostname(self, hostname):

@parameter('resource', ensure_type=twisted.web.resource.Resource)
def _arg_resource(self, resource):

Project details

Release history Release notifications

History Node


This version
History Node


Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Filename, size & hash SHA256 hash help File type Python version Upload date
deconf-0.1.tar.gz (3.6 kB) Copy SHA256 hash SHA256 Source None Apr 25, 2013

Supported by

Elastic Elastic Search Pingdom Pingdom Monitoring Google Google BigQuery Sentry Sentry Error logging CloudAMQP CloudAMQP RabbitMQ AWS AWS Cloud computing Fastly Fastly CDN DigiCert DigiCert EV certificate StatusPage StatusPage Status page