Chapter05/stack_using_array.py - fix bug in pop

[amirsoroush]

The current implementation of pop() in "Chapter05/Stack_using_array.py" file is not correct:

def pop():
  global top
  if top == -1:
    print("Stack Underflow")
  else:
    top = top-1
    data[top] = 0
    return data[top+1]

It first decreases the top and then sets its value to 0 !

What we want it this:

def pop():
    global top
    if top == -1:
        print("Stack Underflow")
    else:
        value = data[top]
        data[top] = 0
        top = top - 1
        return value

We need to first store the value somewhere then set the current position to 0 and then decrease the top and finally return the stored value.

I also applied "Black" formatting to the whole file as it's currently hard to read with 2 spaces indentation.

[amirsoroush]

Since we do not assign to the top, there is no need for global keyword here.

[Yashwanth-K]

Yes. Why there are so many errors in this book?

[amirsoroush]

I tried to contact the author for reviewing the PRs but he didn't respond to my email.