Initialising Queue in Python

Question

I am trying to code my first Queue class. So far I have this code that seemes to work:

class Queue(list):
    def __init__(self):
        self = []

    def insert(self, x):
        self.append(x)
        return self

    def delete(self):
        if len(self) == 0:
            print "The queue is empty"
        else:
            self.remove(self[0])
            return self

However, I was recomended to rewrite it, and when I try something like this I got wrong results:

class Queue:
    def __init__(self):
        self.items = []

    def insert(self, x):
        self.items.append(x)

Test:

queue = Queue()
print queue
queue.insert(5)
print queue

Got:

<__main__.Queue instance at 0x0000000002A2F148>
<__main__.Queue instance at 0x0000000002A2F148>

Could you, please, explain me the difference between two approaches and why the second doesn't work (although I saw it on many websites)?

Second one works, just override` __str__` or do print queue.items — Andrey
– Andrey, Commented Jan 21, 2016 at 12:27
how would you run your first method and what is the expected output of your second method — The6thSense
– The6thSense, Commented Jan 21, 2016 at 12:28
The expected ouputs for the tests (see "Test" above) are [], [5] respectively. I got it using the first code version and following the str advise (Thank you!) with the second code version. — Irina
– Irina, Commented Jan 21, 2016 at 19:53

dlmeetei · Accepted Answer · 2016-01-22 08:10:52Z

1

You need need implement either str or repr for your class Queue before printing

edited Jan 22, 2016 at 8:10

answered Jan 21, 2016 at 12:28

dlmeetei

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Comments

JustDucky · Accepted Answer · 2016-01-21 12:35:56Z

0

Inside the rewrite, you might want to return the value of insert, and in the calling, assign it to a variable:

queue = Queue()
print queue #should show something like <__main__.Queue instance at 0x(some numbers here)>
newQueue = queue.insert(5)
print newQueue

and inside the function, changing it to something like:

def insert(self, x):
    self.items.append(x)
    return self.items

answered Jan 21, 2016 at 12:35

JustDucky

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