How to Implement a Stack Class in Python

class Stack:
    def __init__(self):
        self._items = []

    def push(self, item):
        """Add an item to the top of the stack."""
        self._items.append(item)

    def pop(self):
        """Remove and return the top item. Raises IndexError if empty."""
        if self.is_empty():
            raise IndexError("pop from empty stack")
        return self._items.pop()

    def peek(self):
        """Return the top item without removing it. Raises IndexError if empty."""
        if self.is_empty():
            raise IndexError("peek from empty stack")
        return self._items[-1]

    def is_empty(self):
        """Check if the stack is empty."""
        return len(self._items) == 0

    def size(self):
        """Return the number of items in the stack."""
        return len(self._items)

    def __str__(self):
        """String representation showing stack from bottom to top."""
        return f"Stack({self._items})"


if __name__ == "__main__":
    stack = Stack()
    stack.push(10)
    stack.push(20)
    stack.push(30)
    print(f"Stack after pushes: {stack}")
    print(f"Size: {stack.size()}")
    print(f"Is empty: {stack.is_empty()}")
    print(f"Peek: {stack.peek()}")
    print(f"Pop: {stack.pop()}")
    print(f"Stack after pop: {stack}")
    print(f"Final size: {stack.size()}")