stack = []                                   # on first import
error = 'stack1.error'                       # local exceptions

def push(obj):
    global stack                             # use 'global' to change
    stack = [obj] + stack                    # add item to the front

def pop():	
    global stack
    if not stack:
        raise error, 'stack underflow'       # raise local error
    top, stack = stack[0], stack[1:]         # remove item at front
    return top

def top():
    if not stack:                            # raise local error
        raise error, 'stack underflow'       # or let IndexError occur
    return stack[0] 

def empty():      return not stack           # is the stack []?
def member(obj):  return obj in stack        # item in stack?
def item(offset): return stack[offset]       # index the stack
def length():     return len(stack)          # number entries
def dump():       print '<Stack:%s>' % stack