NetworkX节点属性保存异常问题咨询

从文件读取边列表创建NetworkX的DiGraph图，再从另一文件为部分节点添加date属性（边列表中部分节点无该属性）。设置属性时断言通过，但后续再次校验时，部分应存在date属性的节点断言失败。

代码如下：

import networkx as nx

# Load edges
G = nx.read_edgelist("edges.txt", nodetype=int, create_using=nx.DiGraph)

# Verify load was right
print("Number of nodes:", G.order())
print("Number of edges:", G.size())
print()

num_dates = 0
num_useless = 0
with open("node-dates.txt") as f:
    for line in f:
        if line[0] == "#":
            continue
        nodeID = line.split()[0]
        if nodeID[:2]=="11":
            nodeID = int(nodeID[2:])
        if int(nodeID) in G:
            num_dates += 1
        else:
            num_useless += 1
            G.add_node(int(nodeID))
        G.nodes[int(nodeID)]["date"] = line.split()[1]
        # This below assert passes
        assert(G.nodes[int(nodeID)]["date"] == line.split()[1])

print("Number of nodes:", G.order())
print("Number of nodes with dates:", num_dates+num_useless)
print("Number of nodes with dates and edges:", num_dates)
print("Number of nodes with dates but no edges:", num_useless)
print("Number of nodes with edges but no dates:", G.order()-num_dates-num_useless)

count_failed_assert = 0
with open("node-dates.txt") as f:
    for line in f:
        if line[0] == "#":
            continue
        nodeID = line.split()[0]
        if nodeID[:2]=="11":
            nodeID = int(nodeID[2:])
        try:
            # But this assert fails?
            assert(G.nodes[int(nodeID)]["date"] == line.split()[1])
        except:
            count_failed_assert += 1
print(count_failed_assert)

运行输出：

Number of nodes: 34546
Number of edges: 421578

Number of nodes: 39951
Number of nodes with dates: 38557
Number of nodes with dates and edges: 33152
Number of nodes with dates but no edges: 5405
Number of nodes with edges but no dates: 1394
2446

原因分析 #

核心问题是**node-dates.txt文件中存在重复的节点ID记录**：

• 第一次遍历文件时，每处理一行就设置对应节点的date属性，此时断言是拿当前行的date值和刚设置的属性对比，自然一致，所以断言通过。
• 如果同一个节点ID在文件中出现多次，后面的行会直接覆盖掉之前设置的date属性值。
• 第二次遍历文件时，当遇到该节点ID的早期记录，用该行的date值去对比节点现在的属性（已经被后续行覆盖），就会出现不相等的情况，导致断言失败，最终count_failed_assert的数值就是文件中重复节点ID的出现次数（减去首次出现的次数）。

你可以统计node-dates.txt中重复节点ID的数量，应该和输出的2446一致。

内容的提问来源于stack exchange，提问作者Anili