这个代码运行不出来，错在哪里

很抱歉，之前的代码有一些错误。以下是修正后的Dijkstra算法的Python代码：

import heapq

def dijkstra(graph, start):
    # 初始化距离和前驱字典
    distances = {vertex: float('inf') for vertex in graph}
    distances[start] = 0
    previous_vertices = {vertex: None for vertex in graph}

    # 初始化堆
    vertices = [(0, start)]
    heapq.heapify(vertices)

    while vertices:
        # 取出堆中最小距离的节点
        current_distance, current_vertex = heapq.heappop(vertices)

        # 如果当前距离已经大于记录的距离，则直接跳过
        if current_distance > distances[current_vertex]:
            continue

        # 遍历当前节点的所有邻居
        for neighbor, weight in graph[current_vertex].items():
            distance = current_distance + weight

            # 如果新距离比记录距离小，则更新
            if distance < distances[neighbor]:
                distances[neighbor] = distance
                previous_vertices[neighbor] = current_vertex
                heapq.heappush(vertices, (distance, neighbor))

    return distances, previous_vertices

# 测试代码
graph = {
    'A': {'B': 5, 'C': 1},
    'B': {'A': 5, 'C': 2, 'D': 1},
    'C': {'A': 1, 'B': 2, 'D': 4, 'E': 8},
    'D': {'B': 1, 'C': 4, 'E': 3, 'F': 6},
    'E': {'C': 8, 'D': 3},
    'F': {'D': 6}
}

start_vertex = 'A'
distances, previous_vertices = dijkstra(graph, start_vertex)

print("距离字典:", distances)
print("前驱字典:", previous_vertices)

请确保你已经正确定义了图的邻接关系，并在最后测试代码中指定起始节点。这段代码能够正常运行，并输出距离字典和前驱字典。