Python-堆栈

stack = []

def stack_push():
val = raw_input("push val:")
stack.append(val)

def stack_pop():
if(len(stack) > 0):
return stack.pop(-1)
else:
return None

def stack_show():
print stack

while(True):
cmd = raw_input("enter cmd:")
if(cmd == 'p'):
stack_push()
elif(cmd == 'o'):
val = stack_pop()
if(val != None):
print("pop val :%s" % val)
else:
print "stack is None"
elif(cmd == 's'):
val = stack_show()
elif(cmd == 'q'):
break;
else:
pass