Stack

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class Stack:
    def __init__(self):
        """Initialize an empty stack."""
        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 from the stack.
        Raises IndexError if stack is empty.
        """
        if self.is_empty():
            raise IndexError("Cannot pop from empty stack")
        return self.items.pop()

    def peek(self):
        """
        Return the top item without removing it.
        Raises IndexError if stack is empty.
        """
        if self.is_empty():
            raise IndexError("Cannot peek empty stack")
        return self.items[-1]

    def is_empty(self):
        """Return True 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 __len__(self):
        """Allow len(stack) syntax."""
        return self.size()

    def __str__(self):
        """String representation: bottom -> top."""
        return f"Stack({self.items})"


# Example usage:
if __name__ == "__main__":
    stack = Stack()

    # Push elements
    stack.push(10)
    stack.push(20)
    stack.push(30)
    print(stack)  # Stack([10, 20, 30])

    # Peek at top
    print(stack.peek())  # 30

    # Pop elements
    print(stack.pop())  # 30
    print(stack.pop())  # 20
    print(stack)  # Stack([10])