utilities: add output_graph_png

writes an image representation of a graph to a png file

src/graph_scheduler/utilities.py

@@ -9,6 +9,7 @@
 __all__ = [
     'dependency_dict_to_networkx_digraph', 'disable_debug_logging',
     'enable_debug_logging', 'networkx_graph_to_dependency_dict',
+    'output_graph_png',
 ]
 
 
@@ -184,3 +185,26 @@ def networkx_graph_to_dependency_dict(graph: nx.Graph) -> typing_graph_dependenc
                 res_graph[rec] = set()
             res_graph[rec].add(sender)
     return res_graph
+
+
+def output_graph_png(graph: typing_graph_dependency_dict, filename: str = None):
+    """
+    Writes an image representation of **graph** to file **filename**
+
+    Args:
+        graph: a graph in dependency dict form
+        filename (str, optional): full path of image to write. Appends
+            '.png' if not present. Defaults to
+            'graph-scheduler-figure-<graph id>.png' in the current
+            directory.
+    """
+    ext = '.png'
+    if filename is None:
+        filename = f'graph-scheduler-figure-{id(graph)}{ext}'
+    elif not filename.endswith(ext):
+        filename += ext
+
+    nx_graph = dependency_dict_to_networkx_digraph(graph)
+    pd = nx.drawing.nx_pydot.to_pydot(nx_graph)
+    pd.write_png(filename)
+    print(f'graph_scheduler.output_graph_png: wrote {ext[1:]} to {filename}')