Roles Role based development
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development Python library Python role role-based development

Roles Description

Role based development Roles is a Python library for Role-based development.Pythonic implementation of the DCI (Data Context Interaction) pattern (http://www.artima.com/articles/dci_vision.html).The big difference with mixins is that this role is applied only to the subject instance, not to the subject class (alas, a new class is constructed).Roles can be assigned and revoked. Multiple roles can be applied to an instance. Revocation can happen in any particular order.Using RolesAs a basic example, consider a domain class:>>> class Person(object):... def __init__(self, name):... self.name = name>>> person = Person("John")The instance should participate in a collaboration in which it fulfills a particular role:>>> from roles import RoleType>>> class Carpenter(object):... __metaclass__ = RoleType... def chop(self):... return "chop, chop"Assign the role to the person:>>> Carpenter(person) # doctest: +ELLIPSIS< Person+Carpenter object at 0x... >>>> person # doctest: +ELLIPSIS< Person+Carpenter object at 0x... >The person is still a Person:>>> isinstance(person, Person)True... and can do carpenter things:>>> person.chop()'chop, chop'See roles.py for more examples.FactoriesIn most cases instances will require specific implementations of a certain role. This can be done by decorating the specific role implementations with the assignto() decorator.>>> from roles import assignto>>> @assignto(Person)... class Biker(object):... __metaclass__ = RoleType... def bike(self):... return 'cycle, cycle'>>> Biker(person) # doctest: +ELLIPSIS< Person+Carpenter+Biker object at 0x... >Assigning to a different class instance doesn't work:>>> class Cat(object):... pass>>> Biker(Cat()) # doctest: +ELLIPSISTraceback (most recent call last): ...NoRoleException: No role found for < class 'Cat' > Requirements: · Python

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