Easy and safe cooperative methods
Making super safe, a cooperative methods library
Python’s super is a very useful tool to write cooperative methods. A cooperative method is one such that cooperates with the other overrides in the same hierarchy. A good example is __init__, as all the overrides must be called in class-hierarchy ascending order to properly build an object.
pip install cooper
Making cooperative methods in linear hierarchies is simple, but that is not the case in the presence of multiple inheritance. The problem lies on the fact that the next override to be called is not known at class definition time. James Knight rant against super makes a very clear exposition of the problem and proposes a methodology to use super consistently, if used at all.
We believe that super is very useful and many interesting and expressive programming patterns arise when using horizontal hierarchies extensively. This library is attempt to make these safer and usable in large projects.
from cooper import *
class Base(Cooperative): @cooperate def __init__(self): print "Base.__init__" class Deriv(Base): @cooperate def __init__(self): print "Deriv.__init__" Deriv()
Automatic argument forwarding
class Base(Cooperative): @cooperate def __init__(base_param=None) print "base_param = ", base_param class Deriv(Base): @cooperate def __init__(deriv_param=None) print "deriv_param = ", base_param Base(deriv_param = "Hello", base_param = "world!")
Output::base_param = Hello deriv_param = World!
class Entity(Cooperative): @cooperative def update(self, timer): print "Entity.update" class Player(Entity): @cooperate def update(self, timer): print "Player.update" Player().update(0)
class Abstract(Cooperative): @abstract def method(self): pass class Concrete(Abstract): @cooperate def method(self): print "Concrete.method" try: obj = Abstract() except TypeError: print "Abstract could not be instantiated". obj = Concrete() obj.method()
Output::Abstract could not be instantiated Concrete.method
Compatibility with standard abstract methods
import abc class Abstract(Cooperative): @abc.abstractmethod def method(self): pass Abstract() # Error
class Entity(Cooperative): @cooperative def dispose(self): print "Entity.dispose" class ConcreteEntity(Entity): @post_cooperate def dispose(self): print "ConcreteEntity.dispose" ConcreteEntity().dispose()
Fix arguments to superclass
class TextWidget(Cooperative): @cooperate def __init__(self, color="black", background="white"): print "color = ", color print "background = ", background class ShadedTextWidget(TextWidget): @cooperate_with_params(color="gray") def __init__(self): pass ShadedTextWidget()
Output::color = gray background = white
import random class FunnyTextWidget(TextWidget): @inner_cooperate def __init__(self, next_method): random_color = random.choice(["green", "yellow", "red"]) next_method (color = random_color)
class MockEntity(Entity): @manual_cooperate def update(self, timer, **k): super(MockEntity, self).update(**k) self.updated_called = True
Copyright (c) 2012, 2015 Juan Pedro Bolivar Puente <firstname.lastname@example.org>
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