""" A skeleton of Stack using Python list.
    Students need to complete the implementation.
    CSCI 204, Spring 2020
    Xiannong Meng
"""

class Stack :
    """ A stack class implemented using Python list.
    The end of the list, or list[n-1], is the 'top' of the stack"""
    def __init__( self ):
        """ Create the stack""" 
        self._the_items = list()
  
    def __str__(self):
        '''
        Create and return a string representation for the stack
        '''
        s = "["
        for i in range(len(self._the_items) - 1, -1, -1):
            s += str(self._the_items[i]) + " -> "
        return s
        
    def is_empty( self ):
        """ Check if empty """
        pass
  
    def __len__ ( self ):
        """ Return the length """
        pass

    def peek( self ):
        """ Return the top item of the stack"""
        pass

    def pop( self ):
        """ Return and remove the top element of the stack"""
        # you should make use of the Python list pop() function
        pass

    def push( self, item ):
        """ Add a new item to the top of the stack"""
        # you should make use of the Python list append function
        pass