bpo-47142: Refine Traversable.

.coveragerc

@@ -4,6 +4,7 @@ omit =
 	*/.tox/*
 	*/_itertools.py
 	*/_legacy.py
+	*/simple.py
 
 [report]
 show_missing = True

importlib_resources/abc.py

@@ -55,6 +55,9 @@ class Traversable(Protocol):
     """
     An object with a subset of pathlib.Path methods suitable for
     traversing directories and opening files.
+
+    Any exceptions that occur when accessing the backing resource
+    may propagate unaltered.
     """
 
     @abc.abstractmethod
@@ -90,9 +93,13 @@ def is_file(self) -> bool:
         """
 
     @abc.abstractmethod
-    def joinpath(self, child: StrPath) -> "Traversable":
+    def joinpath(self, *descendants: StrPath) -> "Traversable":
         """
-        Return Traversable child in self
+        Return Traversable resolved with any descendants applied.
+
+        Each descendant should be a path segment relative to self
+        and main contain multiple levels separated by
+        `posixpath.sep` (``/``).
         """
 
     def __truediv__(self, child: StrPath) -> "Traversable":

importlib_resources/simple.py

@@ -99,10 +99,13 @@ def iterdir(self):
     def open(self, *args, **kwargs):
         raise IsADirectoryError()
 
-    def joinpath(self, name):
+    def joinpath(self, *names):
+        if not names:
+            return self
+        name, rest = names[0], names[1:]
         return next(
             traversable for traversable in self.iterdir() if traversable.name == name
-        )
+        ).joinpath(*rest)
 
 
 class TraversableReader(TraversableResources, SimpleReader):