<p>我在StackOverflow上看到过其他这样的例子,但是我不明白任何答案(我还是一个新程序员),也不明白我看到的其他例子看起来和我的很像,否则我不会发布这个问题。</p>
<p>我在Windows7上运行Python3.2。</p>
<p>我以前从来没有遇到过这种情况,我也曾多次这样上课,所以我真的不知道这次有什么不同。唯一的区别是,我没有生成所有的类文件;我得到了一个模板来填写,一个测试文件来尝试。它对测试文件起作用,但对我的文件不起作用。我一直以与测试文件完全相同的方式调用类中的方法(例如,Lineup.size())</p>
<p>这是我的课:</p>
<pre>
class Queue:
# Constructor, which creates a new empty queue:
def __init__(self):
self.__items = []
# Adds a new item to the back of the queue, and returns nothing:
def queue(self, item):
self.__items.insert(0,item)
return
# Removes and returns the front-most item in the queue.
# Returns nothing if the queue is empty.
def dequeue(self):
if len(self.__items) == 0:
return None
else:
return self.__items.pop()
# Returns the front-most item in the queue, and DOES NOT change the queue.
def peek(self):
if len(self.__items) == 0:
return None
else:
return self.__items[(len(self.__items)-1)]
# Returns True if the queue is empty, and False otherwise:
def is_empty(self):
return len(self.__items) == 0
# Returns the number of items in the queue:
def size(self):
return len(self.__items)
# Removes all items from the queue, and sets the size to 0:
def clear(self):
del self.__items[0:len(self.__items)]
return
# Returns a string representation of the queue:
def __str__(self):
return "".join(str(i) for i in self.__items)
</pre>
<p>这是我的程序:</p>
<pre><code>from queue import Queue
Lineup = Queue()
while True:
decision = str(input("Add, Serve, or Exit: ")).lower()
if decision == "add":
if Lineup.size() == 3:
print("There cannot be more than three people in line.")
continue
else:
person = str(input("Enter the name of the person to add: "))
Lineup.queue(person)
continue
elif decision == "serve":
if Lineup.is_empty() == True:
print("The lineup is already empty.")
continue
else:
print("%s has been served."%Lineup.peek())
Lineup.dequeue()
continue
elif (decision == "exit") or (decision == "quit"):
break
else:
print("%s is not a valid command.")
continue
</code></pre>
<p>这是我输入“add”作为决策变量时的错误消息:</p>
<p><em>第8行,in
builtins.AttributeError:“Queue”对象没有属性“size”</em></p>
<p>那么,这是怎么回事?这个有什么不同?</p>