Fix KeyError when networks with no gateway exist

docker-net-graph.py

@@ -63,7 +63,7 @@ def get_networks(client: docker.DockerClient, verbose: bool) -> typing.Dict[str,
 
     for net in sorted(client.networks.list(), key=lambda k: k.name):
         try:
-            gateway = net.attrs["IPAM"]["Config"][0]["Gateway"]
+            gateway = net.attrs["IPAM"]["Config"][0]["Subnet"]
         except (KeyError, IndexError):
             # This network doesn't seem to be used, skip it
             continue

test/docker-compose.yml

@@ -22,6 +22,7 @@ services:
         - network_a
         - network_b
         - network_c
+        - no_gateway
     host_service:
       container_name: host_service
       image: leoverto/dummy-image
@@ -36,3 +37,11 @@ networks:
   network_b:
   network_c:
   empty_network:
+  no_gateway:
+    driver: bridge
+    driver_opts:
+      com.docker.network.bridge.name: br-no-gateway
+    ipam:
+      driver: default
+      config:
+        - subnet: 172.22.1.0/24