cooper 0.1.3

Easy and safe cooperative methods

cooper

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.

Installation

pip install cooper

The problem

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.

Examples

from cooper import *

Cooperative constructors

class Base(Cooperative):
    @cooperate
    def __init__(self):
        print "Base.__init__"

class Deriv(Base):
    @cooperate
    def __init__(self):
        print "Deriv.__init__"

 Deriv()

Output:

Base.__init__
Deriv.__init__

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!

Other methods

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)

Output::

Entity.update
Player.update

Abstract methods

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

Post-cooperation

class Entity(Cooperative):
    @cooperative
    def dispose(self):
        print "Entity.dispose"

class ConcreteEntity(Entity):
    @post_cooperate
    def dispose(self):
        print "ConcreteEntity.dispose"

ConcreteEntity().dispose()

Output::

ConcreteEntity.dispose
Entity.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

Inner cooperation

import random

class FunnyTextWidget(TextWidget):
    @inner_cooperate
    def __init__(self, next_method):
        random_color = random.choice(["green", "yellow", "red"])
        next_method (color = random_color)

Manual cooperation

class MockEntity(Entity):
    @manual_cooperate
    def update(self, timer, **k):
        super(MockEntity, self).update(**k)
        self.updated_called = True

References

• Python’s super is nifty, but you can’t use it

• Python’s method resolution order

License

Copyright (c) 2012, 2015 Juan Pedro Bolivar Puente <[e-mail]>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.