Classes Python and developing Stack

Question

I have created my own LIFO container class Stack that supports the methods of push, len, pop, and a check on isEmpty. All methods appear to be working in my example calls, except for when I call a created instance of this class(in my example s) I receive a memory location for the created object when I want to see the actual contents of that object.

class Stack:

   x = []

    def __init__(self, x=None):
        if x == None:
            self.x = []
        else:
            self.x = x

    def isEmpty(self):
        return len(self.x) == 0
    def push(self,p):
        self.x.append(p)
    def pop(self):
        return self.x.pop()
    def __len__(self):
        return(len(self.x))


    s = Stack()    
    s.push('plate 1')
    s.push('plate 2')
    s.push('plate 3')
    print(s)
    print(s.isEmpty())
    print(len(s))
    print(s.pop())
    print(s.pop())
    print(s.pop())
    print(s.isEmpty())

I get the result of running this line print(s) to be <__main__.Stack object at 0x00000000032CD748>t when I would expect and am looking for ['plate 1','plate 2','plate3']

@deathApril -- Since OP is really just wrapping a list, I assume that this is mostly a learning exercise... — mgilson
– mgilson, Commented Apr 17, 2013 at 22:56
Yes, if this wasn't a learning exercise, list would be fine on its own. — kindall
– kindall, Commented Apr 17, 2013 at 23:14

mgilson · Accepted Answer · 2013-04-17 22:52:30Z

3

You need to also override __str__ or __repr__ if you want your class to have a different representation when printing. Something like:

def __str__(self):
    return str(self.x)

should do the trick. __str__ is what is called by the str function (and implicitly called by print). The default __str__ simply returns the result of __repr__ which defaults to that funny string with the type and the memory address.

answered Apr 17, 2013 at 22:52

mgilson

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1 Comment

CPM Over a year ago

Yep a learning exercise, new to programming and realized something somewhere was defaulting to the memory address, but couldnt figure out how to correctly overide it. Thanks

eandersson · Accepted Answer · 2013-04-24 10:51:12Z

2

You need to override the default implementation of __repr__. Otherwise it will use the default implementation which returns an informal string representation of the class, in this case the type and memory address.

def __repr__(self):
    return str(self.x)

edited Apr 24, 2013 at 10:51

answered Apr 17, 2013 at 22:52

eandersson

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1 Comment

mgilson Over a year ago

Why would you use self.__dict__['x'] when you can just use self.x?

Charles Doutriaux · Accepted Answer · 2015-08-14 06:00:44Z

0

Yes override __str__ and/or __repr__ Remember __repr__ can can evaled and return the same object if possible

edited Aug 14, 2015 at 6:00

answered Apr 17, 2013 at 23:01

Charles Doutriaux

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1 Comment

mgilson Over a year ago

__repr__ can be evaled and return the same object -- That's not exactly true. If possible/practical, it should follow that guideline. But for most real-world objects, this isn't even practical.

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