#~~Author~~. Don Perterson
#~~Email_Address~~. donp@donp.boi.hp.com 
#~~Script_Type~~. Python
#~~Sub_Type~~. Misc
#~~Keywords~~. No Keywords

#~~Comment~~.
#class stack:
#	'''List-based implementation of a stack class.  The stack elements
#	can be any object, sequence, number, etc.
#	
#	The methods are:
#		push(object)	  Push an object onto the stack
#		pop()			 Remove the top of stack and return it
#		is_empty()		Return nonzero if stack is empty
#		num_elements()	Number of elements on stack
#		dump_stack()	  Print stack to stdout, 1 line per element
#	'''

#~~Script~~.

class Stack:
	def __init__(self):
		self.stack = []
	def push(self, object):
		self.stack.append(object)

	def pop(self):
		if len(self.stack) == 0:
			raise "Error", "stack is empty"
		obj = self.stack[-1]
		del self.stack[-1]
		return obj

	def is_empty(self):
		if len(self.stack) == 0:
			return 1
		return 0

	def num_elements(self):
		return len(self.stack)

	def dump_stack(self):
		print "Top of stack is last element in list (number 1)"
		n = len(self.stack)
		fmt = "  %%%dd  %%s" % len(`n + 1`)
		for ix in xrange(n):
			print fmt % (n - ix, self.stack[ix])


if __name__ == "__main__":
	list1 = [1.2, "3.4"]
	s = Stack()
	error = "Error"
	if s.num_elements() != 0:  raise error
	s.push("Hi")
	s.push(4)
	s.push(list1)
	if s.is_empty():  raise error
	s.dump_stack();
	el = s.pop()
	if el != list1:  raise error
	del el
	el = s.pop()
	if el != 4:  raise error
	del el
	el = s.pop()
	if el != "Hi":  raise error
	if not s.is_empty():  raise error