Preserve path to the file when rendering model (#3186)

* Issue #3184

* reverted signature

* os import

* black formatting

* split line

pyro/infer/inspect.py

@@ -2,6 +2,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
 import itertools
+import os
 from collections import defaultdict
 from pathlib import Path
 from types import SimpleNamespace
@@ -572,7 +573,7 @@ def render_model(
         list of tuples for semisupervised models.
     :param model_kwargs: Dict of keyword arguments to pass to the model, or
         list of dicts for semisupervised models.
-    :param str filename: File to save rendered model in.
+    :param str filename: Name of file or path to file to save rendered model in.
     :param bool render_distributions: Whether to include RV distribution
         annotations (and param constraints) in the plot.
     :param bool render_params: Whether to show params inthe plot.
@@ -604,9 +605,9 @@ def render_model(
     graph = render_graph(graph_spec, render_distributions=render_distributions)
 
     if filename is not None:
-        filename = Path(filename)
-        suffix = filename.suffix[1:]  # remove leading period from suffix
-        graph.render(filename.stem, view=False, cleanup=True, format=suffix)
+        suffix = Path(filename).suffix[1:]  # remove leading period from suffix
+        filepath = os.path.splitext(filename)[0]
+        graph.render(filepath, view=False, cleanup=True, format=suffix)
 
     return graph