Picking classes based on given parameters

Question

So i have a class:

class Unit(object):
    def __init__(self, name, x , y, z):
        self.name = name
        self.strength = x + y
        self.intelligence = x + z 
        self.speed = y + z - x

and two species of these Units

class Red(Unit):
    def __init__(self, name, x, y, z):
        Unit.__init__(self,name, x, y, z)
        self.strength = self.strength * 2   

class Blue(Unit):
    def__init__(self, name, x, y, z):
        Unit.__init__(self, name, x, y, z)
        self.speed = self.speed * 2

I want the race to be decided based on what x, y, z, was used as input (z > x means the unit belongs to class Red and x > z means the unit belongs to class Blue) without having to set one before hand, how do I do this?

So you want e.g. `isinstance(Unit(1, 2, 3), Red)` to be `True`? — jonrsharpe, Oct 09 '15 at 14:23
I basically want something that if i plugged in say ben = Class('Ben', 1, 4, 5) it would decide whether ben was part of the Red or Blue class — Danny Quinn, Oct 09 '15 at 14:28
Then yes, you probably want the [*"factory method pattern"*](https://en.wikipedia.org/wiki/Factory_method_pattern) as @xi_ shows. Possible duplicate of http://stackoverflow.com/q/7273568/3001761 — jonrsharpe, Oct 09 '15 at 14:29
Thanks so much, yes was worried this wasn't a good question but wasn't sure what to search for! — Danny Quinn, Oct 09 '15 at 14:36

score 2 · Answer 1 · answered Oct 09 '15 at 14:23

2

You could create function for that:

def builder(name, x, y, z):
    if z > x:
        return Red(name, x, y, z)
    elif x > z:
        return Blue(name, x, y, z)

answered Oct 09 '15 at 14:23

xiº

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Thanks that looks like what I'm looking for, I've basically been using random numbers to generate a players stats and I want these random stats to be used to decide what class to use – Danny Quinn Oct 09 '15 at 14:26

Bryan Oakley · Answer 2 · 2015-10-09T14:31:43.350

0

You can set the __class__ attribute in your __init__:

class Unit(object):
    def __init__(self, name, x , y, z):
        self.name = name
        self.strength = x + y
        self.intelligence = x + z 
        self.speed = y + z - x

        if z > x:
            self.__class__ = Red
        else:
            self.__class__ = Blue

red = Unit("foo", 1,2,3)
blue = Unit("bar", 3,2,1)

You can also create a factory method that instantiates the appropriate class. You can do this as a stand-alone function, or you could make a class method. Here's the stand-alone version:

def unit_factory(name, x, y, z):
    if x > z:
        return Red(name, x, y, z)
    return Blue(name, x, y, z)

red = unit_factory("foo", 1, 2, 3)
blue = unit_factory("bar", 3, 2, 1)

edited Oct 09 '15 at 14:31

answered Oct 09 '15 at 14:26

Bryan Oakley

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Your example didn't match OP condition. `if z > x: else:` is `z > x` or `x<=z` – xiº Oct 09 '15 at 14:33
@xi_ the OP's version (and yours) is undefined for `x == z`, though; you get `None` instead of an instance. – jonrsharpe Oct 09 '15 at 14:34
@x: the OP didn't specify what happens when they are equal. I assumed it had to be one or the other. – Bryan Oakley Oct 09 '15 at 14:35

Picking classes based on given parameters

2 Answers2