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

    def __repr__(self):
        """Return a string representation of the Stack.
        The contents are listed from bottom to top in angle brackets."""
        return str(self.contents).replace('[','<').replace(']','>')

    def is_empty(self):
        """Returns a boolean: whether self is an empty Stack."""
        return self.contents==[]

    def height(self):
        """Returns the number of elements contained in self."""
        return len(self.contents)

    def top(self):
        """Returns the top element of self."""
        assert self.height() > 0
        return self.contents[-1]

    def pop(self):
        """Modifies self by eliminating the top element."""
        assert self.height() > 0
        self.contents.pop()

    def push(self, item):
        """Modifies self by adding a new item on top.
        arguments:
          self -- an RA_stack
          item -- an arbitrary value to be added to the top"""

        self.contents.append(item)

"""
s = Stack()
for e in range(10):
    s.push(e)

print s
print s.top()
s.pop()
print s.top()
s.pop()
print s
"""