Support instance of pathlib.PosixPath as artifact URI (#3468)

Passing an instance of `pathlib.PosixPath` to the `artifacts` attribute of `save_model` results in an `AttributeError: 'PosixPath' object has no attribute 'decode'` exception being thrown by `urllib`.

Explicit conversion to string overcomes this problem. I wonder whether this could be added to `mlflow` directly.

Signed-off-by: Ghislain Vaillant <ghisvail@gmail.com>

mlflow/tracking/artifact_utils.py

@@ -59,7 +59,7 @@ def _download_artifact_from_uri(artifact_uri, output_path=None):
     :param output_path: The local filesystem path to which to download the artifact. If unspecified,
                         a local output path will be created.
     """
-    parsed_uri = urllib.parse.urlparse(artifact_uri)
+    parsed_uri = urllib.parse.urlparse(str(artifact_uri))
     prefix = ""
     if parsed_uri.scheme and not parsed_uri.path.startswith("/"):
         # relative path is a special case, urllib does not reconstruct it properly