deconf 0.1.1

An object system for building declarative configurations in Python.

deconf
======

An object system for building declarative configurations in Python.

A class that has rich(ish) keyword-parameter handling, including
[explicit handling of required parameters](https://github.com/dustinlacewell/deconf#pass-through-parameters),
[declaration of parameter dependencies](https://github.com/dustinlacewell/deconf#dependency-parameters) and
[basic type-checking](https://github.com/dustinlacewell/deconf#type-checked-parameters).

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 + self.foo


Contrived Example:
------------------

class Person(Deconfigurable):
@staticmethod
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 = 'ldlework.com',
domains = [
Domain(
hostname='ldlework.com',
resource=File('/var/txweb/ldlework.com'),
),
Domain(
hostname='lichen.ldlework.com',
resource=ReverseProxyResource('localhost', 8088, ''),
),
],
)


Where Domain is implemented as:

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

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