Harrison/gml save (#1676)

Co-authored-by: Satoru Sakamoto <51464932+satoru814@users.noreply.github.com>

docs/modules/indexes/chain_examples/graph_qa.ipynb

@@ -178,16 +178,16 @@
      "text": [
       "\n",
       "\n",
-      "\u001B[1m> Entering new GraphQAChain chain...\u001B[0m\n",
+      "\u001b[1m> Entering new GraphQAChain chain...\u001b[0m\n",
       "Entities Extracted:\n",
-      "\u001B[32;1m\u001B[1;3m Intel\u001B[0m\n",
+      "\u001b[32;1m\u001b[1;3m Intel\u001b[0m\n",
       "Full Context:\n",
-      "\u001B[32;1m\u001B[1;3mIntel is going to build $20 billion semiconductor \"mega site\"\n",
+      "\u001b[32;1m\u001b[1;3mIntel is going to build $20 billion semiconductor \"mega site\"\n",
       "Intel is building state-of-the-art factories\n",
       "Intel is creating 10,000 new good-paying jobs\n",
-      "Intel is helping build Silicon Valley\u001B[0m\n",
+      "Intel is helping build Silicon Valley\u001b[0m\n",
       "\n",
-      "\u001B[1m> Finished chain.\u001B[0m\n"
+      "\u001b[1m> Finished chain.\u001b[0m\n"
      ]
     },
     {
@@ -205,10 +205,76 @@
     "chain.run(\"what is Intel going to build?\")"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "410aafa0",
+   "metadata": {},
+   "source": [
+    "## Save the graph\n",
+    "We can also save and load the graph."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "id": "bc72cca0",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "graph.write_to_gml(\"graph.gml\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "id": "652760ad",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from langchain.indexes.graph import NetworkxEntityGraph"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "id": "eae591fe",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "loaded_graph = NetworkxEntityGraph.from_gml(\"graph.gml\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 10,
+   "id": "9439d419",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "[('Intel', '$20 billion semiconductor \"mega site\"', 'is going to build'),\n",
+       " ('Intel', 'state-of-the-art factories', 'is building'),\n",
+       " ('Intel', '10,000 new good-paying jobs', 'is creating'),\n",
+       " ('Intel', 'Silicon Valley', 'is helping build'),\n",
+       " ('Field of dreams',\n",
+       "  \"America's future will be built\",\n",
+       "  'is the ground on which')]"
+      ]
+     },
+     "execution_count": 10,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "loaded_graph.get_triples()"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "f70b9ada",
+   "id": "045796cf",
    "metadata": {},
    "outputs": [],
    "source": []

langchain/graphs/networkx_graph.py

@@ -1,6 +1,7 @@
 """Networkx wrapper for graph operations."""
+from __future__ import annotations
 
-from typing import List, NamedTuple, Tuple
+from typing import Any, List, NamedTuple, Optional, Tuple
 
 KG_TRIPLE_DELIMITER = "<|>"
 
@@ -48,7 +49,7 @@ def get_entities(entity_str: str) -> List[str]:
 class NetworkxEntityGraph:
     """Networkx wrapper for entity graph operations."""
 
-    def __init__(self) -> None:
+    def __init__(self, graph: Optional[Any] = None) -> None:
         """Create a new graph."""
         try:
             import networkx as nx
@@ -57,9 +58,25 @@ class NetworkxEntityGraph:
                 "Could not import networkx python package. "
                 "Please it install it with `pip install networkx`."
             )
-
+        if graph is not None:
+            if not isinstance(graph, nx.DiGraph):
+                raise ValueError("Passed in graph is not of correct shape")
+            self._graph = graph
+        else:
             self._graph = nx.DiGraph()
 
+    @classmethod
+    def from_gml(cls, gml_path: str) -> NetworkxEntityGraph:
+        try:
+            import networkx as nx
+        except ImportError:
+            raise ValueError(
+                "Could not import networkx python package. "
+                "Please it install it with `pip install networkx`."
+            )
+        graph = nx.read_gml(gml_path)
+        return cls(graph)
+
     def add_triple(self, knowledge_triple: KnowledgeTriple) -> None:
         """Add a triple to the graph."""
         # Creates nodes if they don't exist
@@ -97,6 +114,11 @@ class NetworkxEntityGraph:
             results.append(f"{src} {relation} {sink}")
         return results
 
+    def write_to_gml(self, path: str) -> None:
+        import networkx as nx
+
+        nx.write_gml(self._graph, path)
+
     def clear(self) -> None:
         """Clear the graph."""
         self._graph.clear()