我的代码出现问题。我一直收到以下错误：
AttributeError: 'NoneType' object has no attribute 'insert'
有人能告诉我为什么会收到此错误吗？这是我的代码和snippit，它导致下面的大多数问题。
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
这是主要的堆函数，我需要从中获取函数。这是给我麻烦的代码的一部分。
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
这是我的PriorityQueue类，它调用函数并帮助我将它们实现为优先级队列。
来自MyHeap导入堆的
class PriorityQueue(object):
def __init__(self):
self.heap = None
def enqueue(self, item, priority):
'''Post: Item is inserted with specified priority in the PQ.'''
self.heap.insert(priority, item)
def first(self):
'''Post: Returns but does not remove the highest priority item from the PQ.'''
return self.heap[0]
def dequeue(self):
'''Post: Removes and returns the highest priority item from the PQ.'''
if Heap.size() is None:
raise ValueError("Error your queue is empty.")
self.first()
self.heap.delete_max()
def size(self):
'''Post: Returns the number of items in the PQ.'''
return Heap.size()
因此在此代码中，enqueue调用insert函数。
def enqueue(self, item, priority):
'''Post: Item is inserted with specified priority in the PQ.'''
self.heap.insert(priority, item)
最后这是我的测试代码：
from PriorityQueue import PriorityQueue
PQ = PriorityQueue()
PQ.enqueue(1, 200)
PQ.enqueue(2, 450)
PQ.enqueue(3, 204)
这可能是一个简单的修复，但是有谁知道为什么我一直得到属性错误？
答案 0 :(得分：1)
这是因为您使用self.heap初始化None：
class PriorityQueue(object):
def __init__(self):
self.heap = None
您可能应该使用Heap()初始化：
class PriorityQueue(object):
def __init__(self):
self.heap = Heap()
您应该只使用一个参数致电self.heap.insert（您正在与两个人打电话）：
def enqueue(self, item, priority):
'''Post: Item is inserted with specified priority in the PQ.'''
self.heap.insert((priority, item))
您应该使用self.heap.size()，而不是Heap.size()：
if self.heap.size() == 0:
raise ValueError("Error your queue is empty.")
以及
def size(self):
'''Post: Returns the number of items in the PQ.'''
return self.heap.size()
您应该从self.heap.delete_max()：
def dequeue(self):
'''Post: Removes and returns the highest priority item from the PQ.'''
if self.heap.size() == 0:
raise ValueError("Error your queue is empty.")
return self.heap.delete_max()
first必须返回堆中的[1]元素，因为[0]总是None：
def first(self):
'''Post: Returns but does not remove the highest priority item from the PQ.'''
return self.heap.heap[1]