[FIXED] Why is my python code to convert an number to binary using stack not working?

Issue

The following is my code to convert a number to binary using stacks written in Python3. Whenever I run it, None is produced as the output. What might be causing this? Thanks in advance.

class Stack():
    def __init__(self):
        self.stack = []
        self.top = -1

def push(self, val):
    self.stack.append(val)
    self.top += 1

def pop(self):
    if self.top == -1:
        print('Underflow')
    else:
        del self.stack[self.top]
        self.top -= 1

def empty(self):
    return self.stack == []

def peek(self):
    return self.top

def display(self):
    return self.stack

def binary(n):
    b = Stack()
    while n > 0:
        r = n%2
        b.push(r)
        n = n//2

    bn = ''
    while not b.empty():
        bn += str(b.pop())

    return bn

print(binary(242))

Solution

This line just pops the elements from the stack and does not return anything.It returns None.

bn += str(b.pop()) 

You must store the top element in a variable and then pop the stack after it.

Try this below in your binary function :

def binary(n):
    b = Stack()
    while n > 0:
        r = n % 2
        b.push(r)
        n = n//2
    print(b.stack)
    bn = ''
    while not b.empty():
        bn += str(b.stack[-1])
        b.pop()
    return bn

Answered By - Abhishek Kulkarni

Answer Checked By - David Marino (PHPFixing Volunteer)