[py parsing] Accept pathlib.Path for paths (#22936)

Author: jwnimmer-tri

bindings/pydrake/multibody/parsing_py.cc

@@ -130,15 +130,8 @@ PYBIND11_MODULE(parsing, m) {
             cls_doc.scene_graph.doc)
         .def("package_map", &Class::package_map, py_rvp::reference_internal,
             cls_doc.package_map.doc)
-        .def(
-            "AddModels",
-            // Pybind11 won't implicitly convert strings to
-            // std::filesystem::path, but C++ will. Use a lambda to avoid wider
-            // disruptions in python bindings.
-            [](Parser& self, const std::string& file_name) {
-              return self.AddModels(file_name);
-            },
-            py::arg("file_name"), cls_doc.AddModels.doc)
+        .def("AddModels", &Class::AddModels, py::arg("file_name"),
+            cls_doc.AddModels.doc)
         .def("AddModelsFromUrl", &Class::AddModelsFromUrl, py::arg("url"),
             cls_doc.AddModelsFromUrl.doc)
         .def("AddModelsFromString", &Class::AddModelsFromString,

bindings/pydrake/multibody/test/parsing_test.py

@@ -23,6 +23,7 @@
 
 import copy
 import os
+from pathlib import Path
 import re
 import unittest
 
@@ -124,8 +125,8 @@ def test_parser_file(self):
         urdf_file = FindResourceOrThrow(
             "drake/multibody/benchmarks/acrobot/acrobot.urdf")
         for dut, file_name in (
-                (Parser.AddModels, sdf_file),
-                (Parser.AddModels, urdf_file),
+                (Parser.AddModels, Path(sdf_file)),
+                (Parser.AddModels, str(urdf_file)),
                 ):
             plant = MultibodyPlant(time_step=0.01)
             parser = Parser(plant=plant)
@@ -255,16 +256,16 @@ def test_scoped_frame_names(self, T):
         GetScopedFrameByName(plant, "world")
         GetScopedFrameByNameMaybe(plant, "world")
 
-    def _make_plant_parser_directives(self):
+    def _make_plant_parser_directives(self, *, path_type=Path):
         """Returns a tuple (plant, parser, directives) for later testing."""
-        model_dir = os.path.dirname(FindResourceOrThrow(
+        model_dir = Path(FindResourceOrThrow(
             "drake/multibody/parsing/test/"
-            "process_model_directives_test/package.xml"))
+            "process_model_directives_test/package.xml")).parent
         plant = MultibodyPlant(time_step=0.01)
         parser = Parser(plant=plant)
         parser.package_map().PopulateFromFolder(model_dir)
-        directives_file = model_dir + "/add_scoped_top.dmd.yaml"
-        directives = LoadModelDirectives(directives_file)
+        directives_file = model_dir / "add_scoped_top.dmd.yaml"
+        directives = LoadModelDirectives(path_type(directives_file))
         return (plant, parser, directives)
 
     def test_load_model_directives_from_string(self):
@@ -296,7 +297,11 @@ def test_process_model_directives(self):
 
     def test_process_model_directives_dispreferred(self):
         """Check the Process... overload that also passes a MbP."""
-        (plant, parser, directives) = self._make_plant_parser_directives()
+        (plant, parser, directives) = self._make_plant_parser_directives(
+            # Use this opportunity to also test a non-standard argument type
+            # for LoadModelDirectives().
+            path_type=str,
+        )
         added_models = ProcessModelDirectives(
             directives=directives, plant=plant, parser=parser)
         model_names = [model.model_name for model in added_models]

multibody/parsing/process_model_directives.cc

@@ -191,9 +191,10 @@ std::vector<ModelInstanceInfo> ProcessModelDirectives(
   return added_models;
 }
 
-ModelDirectives LoadModelDirectives(const std::string& filename) {
+ModelDirectives LoadModelDirectives(const std::filesystem::path& filename) {
+  const std::string filename_str = filename.string();
   return multibody::internal::LoadModelDirectives(
-      {DataSource::kFilename, &filename});
+      {DataSource::kFilename, &filename_str});
 }
 
 ModelDirectives LoadModelDirectivesFromString(

multibody/parsing/process_model_directives.h

@@ -13,7 +13,7 @@ namespace drake {
 namespace multibody {
 namespace parsing {
 
-ModelDirectives LoadModelDirectives(const std::string& filename);
+ModelDirectives LoadModelDirectives(const std::filesystem::path& filename);
 
 ModelDirectives LoadModelDirectivesFromString(
     const std::string& model_directives);