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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):

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