Consider the following Python stack implementation:

class Stack$($object$)$:

def $\_\_$init$\_\_($self$)$:

self.items $=[]$

def push$($self$,$ item$)$:

self.items.append$($item$)$

def pop$($self$)$:

return self.items.pop$()$

def top$($self$)$:

return self.items$[-1]$

def size$($self$)$:

return len$($self$.$items$)$

As implemented above, what is the complexity of the stack class operations?