谷歌 colab 上的 Python Class

Question

Why my code can only print until 3, then I get 0 after all?

Can anyone help me with this question?

I don't know where is the Error.

Thank you!

Here are my code:

class Queue:
  def __init__ (self,size):
    self.__contents = [0] * 10
    self.__head = 0
    self.__count = -1
  
  def is_full(self):
    return self.__head > len(self.__contents)

  def is_empty(self):
    return self.__head == 0

  def add(self, x):
    if self.is_full():
      return
    else:
      self.__contents[self.__head] = x
      self.__head += 1
  
  def get(self):
    if self.is_empty():
      return
    else:
      self.__head -= 1
      self.__count += 1
      return self.__contents[self.__count]

Here are my result:

my_queue = Queue(5)
my_queue.add(4)
my_queue.add(10)
my_queue.add(3)
print(my_queue.get()) # should print 4 I get 4. Success!
print(my_queue.get()) # should print 10 I get 10. Success!
my_queue.add(7)
print(my_queue.get()) # should print 3 I get 3. Success!
my_queue.add(6)
my_queue.add(5)
my_queue.add(4)
my_queue.add(3)     # should print 7 but I get 0. Fail
print(my_queue.get()) # should print 6 but I get 0. Fail
print(my_queue.get()) # should print 5 but I get 0. Fail
print(my_queue.get()) # should print 4 but I get 0. Fail
print(my_queue.get()) # should print 3 but I get 0. Fail

Answer 1

self.__head is the index of the newest element + 1 and you don't actually remove any element from the queue when calling the get method. There is no need to decrease self.__head inside the get method. Doing that next added element will replace the old ones. Remove "self.__head -= 1" and everything will work (as long as you won't add more than 10 elements to the queue).

However, array based queue is a bad idea. To implement a queue you should use something like linked lists.