CODEWITHSUNDEEP
python
Benjamin
Benjamin

Reputation: 308

Pythonic way to switch object "behind the scenes"

I know about the nature of python object names being nothing but "labels" that can be attached to any object and that variables are always passed by reference. But what if I need a different behavior?

To illustrate this, I made a Short example:

class car:
    def __init__(self, brand):
        self.brand = brand

subaru = car("subaru")
toyota = car("toyota")

current_car = subaru
current_brand = current_car.brand

print (current_brand)

current_car = toyota

print (current_brand)

The Output I get is:

subaru
subaru

This doesn't surprise me. However in the project I'm working on right now, I would like to express a selection by making current_car the selected car. Also I would like the object current_brand to always hold the brand of the current car without explicitly doing:

current_brand = current_car.brand

every time I switch the current car. I thought about using a property decorator for this, but I am not shure, that that's the right way. Is there a pythonic way to do this or am I thinking in the wrong direction all-together?

Upvotes: 1

Views: 61

Answers (2)

Benjamin
Benjamin

Reputation: 308

Well, it turns out, that I had a weird knot in my brain, which was keeping me from understanding even the simplest basics of programming. For the unlikely chance someone else goes down the same dead end road of thinking (and happens to find this post) here is what I meant to do:

class car:
    def __init__(self, brand):
        self.brand = brand

subaru = car("subaru")
toyota = car("toyota")

current_car = subaru

def current_brand():
    return current_car.brand

print (current_brand())

current_car = toyota

print (current_brand())

I didn't get that all I tried to do was to have a function that gives me the current_car's brand.

Well, maybe I should take a break and go outside for a while...

Upvotes: 1

Serge Ballesta
Serge Ballesta

Reputation: 149085

I can only think of a __repr__ trick: when you display, print or convert an object to a string, you use its __repr__ method to do the conversion. Here, you could try:

class CurrentBrand:
    def __repr__(self):
        return current_car.brand
current_brand = CurrentBrand()

Now if you do:

subaru = car("subaru")
toyota = car("toyota")

current_car = subaru
print (current_brand)

current_car = toyota
print (current_brand)

The output will be as expected:

subaru
toyota

The limits of the trick are that any direct assignement to current_car will break the magic, and that it is not a string...

Upvotes: 1

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