QGIS上でnetworkxを使い最短経路を取得したい

前提・実現したいこと

QGIS,Pythonともに初心者です。
QGISにて、nx.has_pathを用いて最短距離の検索を試みております。

エラーメッセージ

Traceback (most recent call last):
  File "C:\PROGRA~1\QGIS3~1.14\apps\Python37\lib\code.py", line 90, in runcode
    exec(code, self.locals)
  File "<input>", line 1, in <module>
  File "<string>", line 22, in <module>
  File "C:\PROGRA~1\QGIS3~1.14\apps\Python37\lib\site-packages\networkx\algorithms\shortest_paths\generic.py", line 40, in has_path
    nx.shortest_path(G, source, target)
  File "C:\PROGRA~1\QGIS3~1.14\apps\Python37\lib\site-packages\networkx\algorithms\shortest_paths\generic.py", line 170, in shortest_path
    paths = nx.bidirectional_shortest_path(G, source, target)
  File "C:\PROGRA~1\QGIS3~1.14\apps\Python37\lib\site-packages\networkx\algorithms\shortest_paths\unweighted.py", line 223, in bidirectional_shortest_path
    raise nx.NodeNotFound(msg.format(source, target))
networkx.exception.NodeNotFound: Either source [4000526.346593578, 305276.0959658007, 1413147649, 138.836068, 36.129911] or target [4000423.8004078707, 305864.23483348615, 1413147088, 138.842625, 36.129105] is not in G

該当のソースコード

Python
1import networkx as nx
2
3layer = iface.activeLayer()　###現在のレイヤを取得
4features = layer.getFeatures()　　###レイヤ内の地物を取得
5
6G = nx.read_shp(str(iface.mapCanvas().currentLayer().source()))　##レイヤをグラフとして取得
7
8for f in features:
9    atrib = f.attributes()
10    if atrib[2] == 4585630021:　###始点ノードを取得
11        a = f.attributes()
12    if atrib[2] == 2815748288:　###終点ノードを取得
13        b = f.attributes()
14        
15print(str(a))
16print(str(b))
17
18Shotest_Route = nx.has_path(G, source = a, target = b)