我创建了一个优先级队列，其功能使用我的二进制堆函数。但是，在我的测试文件中，我试图打印出我的队列，看起来像这样。
Your queue looks like this: 15 -> 45 -> 10 -> 100
在某个地方，但是它会一直打印出存储队列的位置而不是队列中的项目，例如：
<PriorityQueue.PriorityQueue object at 0x01E95530>
我读了pythonDocs并得出结论我需要一个 str 函数。但是，我在创建它时遇到问题任何人都可以帮我解决它的样子吗？非常感谢。这是我的全部代码。
class Heap(object):
def __init__(self, items=None):
'''Post: A heap is created with specified items.'''
self.heap = [None]
if items is None:
self.heap_size = 0
else:
self.heap += items
self.heap_size = len(items)
self._build_heap()
def size(self):
'''Post: Returns the number of items in the heap.'''
return self.heap_size
def _heapify(self, position):
'''Pre: Items from 0 to position - 1 satisfy the Heap property.
Post: Heap Property is satisfied for the entire heap.'''
item = self.heap[position]
while position * 2 <= self.heap_size:
child = position * 2
# If the right child, determine the maximum of two children.
if (child != self.heap_size and self.heap[child+1] > self.heap[child]):
child += 1
if self.heap[child] > item:
self.heap[position] = self.heap[child]
position = child
else:
break
self.heap[position] = item
def delete_max(self):
'''Pre: Heap property is satisfied
Post: Maximum element in heap is removed and returned. '''
if self.heap_size > 0:
max_item = self.heap[1]
self.heap[1] = self.heap[self.heap_size]
self.heap_size -= 1
self.heap.pop()
if self.heap_size > 0:
self._heapify(1)
return max_item
def insert(self, item):
'''Pre: Heap Property is Satisfied.
Post: Item is inserted in proper location in heap.'''
self.heap_size += 1
# extend the length of the list.
self.heap.append(None)
position = self.heap_size
parent = position // 2
while parent > 0 and self.heap[parent] < item:
# Move the item down.
self.heap[position] = self.heap[parent]
position = parent
parent = position // 2
# Puts the new item in the correct spot.
self.heap[position] = item
def _build_heap(self):
''' Pre: Self.heap has values in 1 to self.heap_size
Post: Heap property is satisfied for entire heap. '''
# 1 through self.heap_size.
for i in range(self.heap_size // 2, 0, -1): # Stops at 1.
self._heapify(i)
def heapsort(self):
'''Pre: Heap Property is satisfied.
Post: Items are sorted in self.heap[1:self.sorted_size].'''
sorted_size = self.heap_size
for i in range(0, sorted_size -1):
# Since delete_max calls pop to remove an item, we need to append a dummy value to avoid an illegal index.
self.heap.append(None)
item = self.delete_max()
self.heap[sorted_size - i] = item
上面是我的Heap类，我的PriorityQueue取自： 下面是我的PQ类和我的测试文件。
#PriorityQueue.py
from MyHeap import Heap
class PriorityQueue(object):
def __init__(self):
self.heap = Heap()
def enqueue(self, priority, item):
'''Post: Item is inserted with specified priority in the PQ.'''
self.heap.insert((priority, item))
return item
def first(self):
'''Post: Returns but does not remove the highest priority item from the PQ.'''
return self.heap.size()
def dequeue(self):
'''Post: Removes and returns the highest priority item from the PQ.'''
if self.heap.size() is None:
raise ValueError("Error your queue is empty.")
x = self.first()
self.heap.delete_max()
return x
def size(self):
'''Post: Returns the number of items in the PQ.'''
return self.heap.size()
from PriorityQueue import PriorityQueue
PQ = PriorityQueue()
print(PQ.enqueue(1, 10))
print(PQ.enqueue(2, 5))
print(PQ.enqueue(3, 90))
print PQ
print(PQ.size())
def __str__(self):
return str(self.heap)
这只打印出来：
<MyHeap.Heap object at 0x01E255F0>
答案 0 :(得分：2)
好的，__str__的想法是返回某种以人类可读的方式表示对象的字符串。您必须构造字符串，然后将打印而不是
<PriorityQueue.PriorityQueue object at 0x01E95530>
在您的情况下，我们必须退回由self.heap.heap分隔的->项。这可以像你描述的那样获得输出：
def __str__(self):
if self.size():
heap_items = [str(i) for i in self.heap.heap if i]
heap_items_str = ' -> '.join(heap_items)
return "Your queue looks like this: {}".format(heap_items_str)
else:
return "Your queue is empty."
请注意，我们使用的是self.heap.heap，而不是self.heap，因为在这种情况下self是PriorityQueue个实例，而PriorityQueue的.heap属性包含一个Heap。这个Heap我们实际上想要打{{1}}，这反过来又为我们提供了我们正在寻找的列表。
答案 1 :(得分：0)
编辑：我尝试执行以下操作：
def __str__(self): return str(self.heap)
相反，试试这个：
def __str__(self):
return self.heap.__str__()