帮我用python写一段实现Dijkstra算法的代码

以下是一个简单的 Python 实现 Dijkstra 算法的示例代码：

import heapq

def dijkstra(graph, start):
    distances = {node: float('inf') for node in graph}
    distances[start] = 0
    pq = [(0, start)]
    while pq:
        (cost, current_node) = heapq.heappop(pq)
        if cost > distances[current_node]:
            continue
        for neighbor, neighbor_cost in graph[current_node].items():
            new_cost = distances[current_node] + neighbor_cost
            if new_cost < distances[neighbor]:
                distances[neighbor] = new_cost
                heapq.heappush(pq, (new_cost, neighbor))
    return distances

# 示例
graph = {
    'A': {'B': 1, 'C': 4},
    'B': {'A': 1, 'C': 2, 'D': 5},
    'C': {'A': 4, 'B': 2, 'D': 1},
    'D': {'B': 5, 'C': 1}
}

print(dijkstra(graph, 'A'))

运行结果：

{'A': 0, 'B': 1, 'C': 3, 'D': 4}