请用Python程序语言求给定正权有向图的单源最短路径长度。图中包含 n 个顶点，编号为0至n−1，以顶点0作为源点，计算源点到各个顶点的最短路径长度。

在Python中，我们可以使用Dijkstra算法来求解这个问题。Dijkstra算法是一种用于寻找带权重有向图中两个节点之间最短路径的算法。以下是使用`networkx`库实现的一个简单示例：

import networkx as nx

# 假设我们有一个字典表示图的邻接权重
graph = {
    '0': {'1': 3, '2': 5},
    '1': {'2': 1, '3': 4},
    '2': {'3': 2},
    '3': {}
}

def dijkstra(graph, source):
    distances = {node: float('infinity') for node in graph}
    distances[source] = 0
    shortest_path = {}

    visited = set()
    while not visited == set(distances.keys()):
        min_distance_node = None
        for node, distance in distances.items():
            if node not in visited and (min_distance_node is None or distance < distances[min_distance_node]):
                min_distance_node = node

        if min_distance_node is None:
            break

        visited.add(min_distance_node)
        for neighbor, weight in graph[min_distance_node].items():
            new_distance = distances[min_distance_node] + weight
            if new_distance < distances[neighbor]:
                distances[neighbor] = new_distance
                shortest_path[neighbor] = min_distance_node

    return distances, shortest_path

shortest_distances, path = dijkstra(graph, 0)

print("源点0到各顶点的最短距离:")
for vertex, dist in shortest_distances.items():
    print(f"顶点{vertex}: {dist}")

print("\n从源点0到每个顶点的最短路径:")
for dest, src in path.items():
    print(f"从0到{dest}的路径: {src}->{dest}")