CODEWITHSUNDEEP
pythonclassstack
JiaJia
JiaJia

Reputation: 3

stack class in Python

I have written the below code to implement the stack class instead of using the build in function, not sure if I have got it rigth. Can someone please check for me and advise if there is an error?

class DSAStack():

    maxCap = 100

    def __init__(self):
        self.stack = []

        self.count = 0


    def isEmpty(self):
        if self.count == 0:
            return True
        else:
            return false


    def isFull(self):
        if self.count == maxCap:
            return True
        else:
            return false


    def push(self, item):
        if self.isFull:
            raise ('Stack is full...')
        else:
            self.stack[self.count] = item
            self.count += 1


    def pop(self):
        self.topVal = self.top
        self.stack[self.count - 1] = 0
        self.count = self.count - 1

        return self.topVal


    def top(self):
        if self.isEmpty:
            raise ('Stack is empty...')
        else:
            self.top = self.stack[self.count - 1]

Upvotes: 0

Views: 1524

Answers (1)

Akshath Mahajan
Akshath Mahajan

Reputation: 248

Firstly, you need not keep track of count. Accessing the length of the list will do that for you.

def __init__(self):
    self.stack =[]

Now, your logic for isEmpty and isFull was alright, but since we are removing the self.count variable, here's how you'd go about it

def isEmpty(self):
    return len(self.stack) == 0 #Directly return true or false

def isFull(self):
    return len(self.stack) == maxCap #Directly return true or false

In your push function, there are a few things I'd like to point out. First, you need to call the isFull function. So we need to add parentheses to it.

Secondly, you cant just raise ('Stack is full...'), you will get a TypeError: Exceptions must derive from BaseException. This basically means what you raise must be some type of error.

Lastly, you can't add a new element by doing self.stack[self.count]=item since you will get an IndexError

Here are the changes:

def push(self,item):
    if self.isFull():    #Need to call the function, self.isFull is not a variable
        raise Exception('Stack is full...') #Or any other type of error
    else:
        self.stack.append(item)    #Adds new item to the end of self.stack

Now coming to the pop function, setting a value to zero in a list does not really get rid of it. And it can cause a lot of confusion, especially since we are using the len(self.stack) to implement this. Here's how you would pop:

def pop(self):
    if self.isEmpty():
        raise Exception('Stack is empty...')
    else:
        return self.stack.pop() #List has a built-in pop method

So now we don't really need the top function. And that concludes that. Btw, in your top function, you have defined self.top = self.stack[self.count-1] Giving the same name to a function and a variable is never really a good idea.

To implement the pop functionality yourself, you could do the following:

def pop(self):
    if self.isEmpty():
        raise Exception('Stack is empty...')
    else:
        topVal = self.stack[-1] #-1 gives you the last element
        #if stack will contain objects instead of primitive data types, use self.stack[-1].copy()
        del self.stack[-1] #Deletes the element
        return topVal

Polishing your top function will be like this:

def top(self):
    if self.isEmpty():
        raise Exception('Stack is empty...')
    else:
        return self.stack[-1]
def pop(self):
    topVal = self.top()
    del self.stack[-1]    
    return topVal

Note how the top function is defined before the pop function. Also, try to test the code out and resolving any issues.

Upvotes: 1

Related Questions