Accessor & Mutator methods (Python)

Question

I am trying to figure out encapsulation in Python. I was doing a simple little test in shell to see how something worked and it doesn't work like I was expecting. And I can't get it to work. Here's my code:

class Car:
    def __init__(self, carMake, yrMod):
        self.__make = carMake
        self.__yearModel = yrMod
        self.__speed = 0

    #Mutator Methods
    def set_make(self, make):
        self.__make = carMake

    def set_model(self, yrMod):
        self.__yearModel = yrMod

    #def set_speed(self, speed):
        #self.__speed = speed

    #Accessor Methods
    def get_make(self):
        return self.__make

    def get_yearModel(self):
        return self.__yearModel

    def get_speed(self):
        return self.__speed

myCar=Car('Ford', 1968)
myCar2=Car('Nissan', 2012)
myCar.get_make()
'Ford'
myCar.set_make=('Porche')
myCar.get_make()
'Ford'

Why doesn't myCar.set_make change Ford into Porche? Thank you.

What's with all these underscores in your instance attributes, e.g. `self.__speed`? And why are you making all these methods anyhow? What advantage do you think `myCar.set_make("Porsche")/myCar.get_make()` will offer over `myCar.make = 'Porsche'` and `myCar.make`? — DSM, Apr 07 '13 at 20:56
There is never a reason to expose an API like this. There is sometimes a reason to have getter/setter methods, but they should be hidden using the built-in `property`. And since that makes them like normal attributes from the client code's perspective, you should just use those (rather than trivial getters/setters) until you need logic. — , Apr 07 '13 at 20:57

score 9 · Accepted Answer · edited May 23 '17 at 12:31

9

With myCar.set_make=('Porche'), you are setting this member the Car class as the 'Porche' string, but you are not calling the method.

Just remove the = to solve it:

myCar.set_make('Porche')
myCar.get_make() # Porche

Besides, as @DSM points out, there is an error in the argument of set_make:

def set_make(self, make):
    self.__make = make # carMake is not defined!

However, this use of getters and setters in Python is strongly discouraged. If you need something similar for any reason, consider using properties.

edited May 23 '17 at 12:31

Community

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answered Apr 07 '13 at 20:54

A. Rodas

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There's also a bug in `set_make` (`carMake` instead of `make`) so it won't quite work yet, but you're right about the main problem. – DSM Apr 07 '13 at 20:57
Thank you for that, but for some reason I get an error message: – user2255444 Apr 07 '13 at 20:57
This was my first time using this resource, I just started an intro to programming class, so thank you for your patience! – user2255444 Apr 07 '13 at 21:16

score -1 · Answer 2 · edited Aug 18 '14 at 22:24

-1

new_car = Car(...)
new_car2 = Car(...)

new_car._make = 'Ford'
new_car2.make = 'Jetta'

print new_car._make
print new_car2.make

edited Aug 18 '14 at 22:24

Artjom B.

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answered Aug 18 '14 at 22:06

Tim Conroy

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And what value does this answer add to the question? Since you took the time to post this as an answer to a year old question I'm curious. – EWit Aug 18 '14 at 22:29

Accessor & Mutator methods (Python)

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