Added graph store and read functionality

compiler/base/timing_graph.py

@@ -1,6 +1,7 @@
 import copy
 from collections import defaultdict
 import debug
+import json
 
 
 class timing_graph():
@@ -139,6 +140,35 @@ class timing_graph():
 
         return [self.edge_mods[(path[i], path[i+1])] for i in range(len(path)-1)]
 
+    def write(self, filename):
+        """
+        Export graph to a JSON file
+        """
+        # TODO: Find a proper way to store edge_mods values
+        with open(filename, 'w') as f:
+            f.write(
+                json.dumps(
+                    {
+                        'graph':
+                            {key: list(val) for key, val in self.graph.items()},
+                        'edge_mods':
+                            {
+                                ', '.join(key): str(value)
+                                for key, value in self.edge_mods.items()
+                            }
+                    }
+                )
+            )
+
+    def read(self, filename):
+        """
+        Read graph from JSON file
+        """
+        with open(filename, 'r') as f:
+            d = json.loads(f.read())
+            self.graph = {key: set(value) for key, value in d['graph'].items()}
+            self.edge_mods = {tuple(key.split(', ')): value for key, value in d['edge_mods'].items()}
+
     def __str__(self):
         """ override print function output """