Python instance reference accessing method

Question

I'm new to programming so please bear with me if this is obvious.

I have two classes in the same *.py file. the snippets are below. I am trying to simulate a lift, with customers, and in the main program I will create n customers. I would like the method in the elevator class, called startLift to be able to access the individual instances of customer but I am unsure how to do this, so if I loop through my customers, calling the startLift on each iteration, how can I make it so it references this instance.

Thank you in advance.

class elevator:

def __init__(self):

    self.stops = building.getFloors(redbrick)

    if self.stops <1:
        print "elevator out of bounds"
    else:
        print "elevator has ",building.getFloors(redbrick),"stops"

i try rephrase the question :

self.stops = building.getFloors(redbrick)

im calling the building method with in the elevator class, so the building passes information to the elevator class regarding how many floors it can travel.

"redbrick" is an instance of the buliding class, in order for that to work "building.getfloors() , i must pass an instance of the builiding in, or else i get

"unbound method getFloors() must be called with building instance as first argument (got nothing instead)"

but how do i pass in multiple instances of a building into "building.getfloors()if i create it e.g

whitebrick = building()

redbrick = building()

yellowbrick = building()

You appear to be confusing static methods and instance methods. Specifically with customer.getLocation(users). You'll probably want to pass in an instance of a customer into startLift — Moshe
– Moshe, Commented Apr 3, 2013 at 19:53
Thank you for you coming back to me, maybe i didnt explain the question properly but what you said in your reply about passing instances of the customer to the start lift, how do i do that customer.getLocation(users),in this case "user" is an instance of the class customer, but if make multiple instances of the class , how to i make it reference customer.getlocaton() — user2242052
– user2242052, Commented Apr 3, 2013 at 20:02
elevator and customer are both classes. However, you want to create instances of each of those classes. It will be easier to help you if you add in your full code here, as this code will need some significant changes to work properly. — Moshe
– Moshe, Commented Apr 3, 2013 at 20:45
Furthermore your naming conventions are making this harder to understand. Every time you refer to "customer" we can't tell if you mean the class customer, an instance of the class, or the parameter used to instantiate the class customer. Maybe rename the class "Customer" and the parameter "customer_name" or whatever it is supposed to be. — Ethan Coon
– Ethan Coon, Commented Apr 3, 2013 at 20:50

Ethan Coon · Accepted Answer · 2013-04-03 23:21:13Z

I'm going to break the cardinal rule of SO here by not actually answering the question in this answer, but it's too long to be a comment.

Part of the issue seems to be a misunderstanding in how classes and instances work with python or in programming in general (there's nothing wrong with this, we all learn sometime). As a result, your question is valid, but posed pretty awkwardly, so let's step back a second.

Your current init() method for elevator doesn't really work as described. In order to get access to the building, you have to give it to the elevator's init(). For instance, your Building and Elevator classes (which I'm capitalizing to indicate it is a class, and not an instance of that class), might look like this:

class Building:
    def __init__(self, floors=1, color=None):
        self.floors = floors
        self.color = color

    def getFloors(self):
        return self.floors


class Elevator:
    def __init__(self, building):
        self.stops = building.getFloors()
        self.current_floor = 1

Then, in your main program, you'll have something like:

redbrick = Building(floors=4, color='red')
redbrick_elevator = Elevator(redbrick)

Note my capitalization convention -- building is a parameter to elevator's init() method, and is an instance of the class Building. When I call the method getFloors(), it is called on the instance, not the class, and the instance redbrick is passed as self to getFloors() automatically.

Now, your old (pre-edit) customer class was fine (but I would have called it Customer). But the method calling the elevator would not have worked, because the customer was not passed in. So, for instance, you might have something like:

class Elevator:
    def __init__(self, building):
        self.stops = building.getFloors()
        self.current_floor = 1
        self.customer_list = []
        self.stop_list = []

    def getCurrentFloor(self):
        return self.current_floor

    def callElevator(self, floor):
        self.stop_list.append(floor)

    def getOn(self, customer):
        self.customer_list.append(customer)
        self.stop_list.append(customer.getEndFloor())

    def letOff(self):
        for customer in self.customer_list[:]:
            if self.current_floor == customer.getEndFloor():
                self.customer_list.remove(customer)

...

Hopefully this is enough to get you started, both with some of the ideas of how classes and instances work in python and in one simple way of storing relationships between instances of different classes.

If you're happy with the answer, you should click the check mark to accept it :) And welcome to SO!

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