2 files changed, 27 insertions, 6 deletions
diff --git a/Lib/pathlib.py b/Lib/pathlib.py
index 1480e2fc71a..a06676fbe4f 100644
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -634,13 +634,16 @@ class PurePath(object):
         for a in args:
             if isinstance(a, PurePath):
                 parts += a._parts
-            elif isinstance(a, str):
-                # Force-cast str subclasses to str (issue #21127)
-                parts.append(str(a))
             else:
-                raise TypeError(
-                    "argument should be a path or str object, not %r"
-                    % type(a))
+                a = os.fspath(a)
+                if isinstance(a, str):
+                    # Force-cast str subclasses to str (issue #21127)
+                    parts.append(str(a))
+                else:
+                    raise TypeError(
+                        "argument should be a str object or an os.PathLike "
+                        "object returning str, not %r"
+                        % type(a))
         return cls._flavour.parse_parts(parts)
 
     @classmethod
@@ -693,6 +696,9 @@ class PurePath(object):
                                                   self._parts) or '.'
             return self._str
 
+    def __fspath__(self):
+        return str(self)
+
     def as_posix(self):
         """Return the string representation of the path with forward (/)
         slashes."""
@@ -943,6 +949,10 @@ class PurePath(object):
                 return False
         return True
 
+# Can't subclass os.PathLike from PurePath and keep the constructor
+# optimizations in PurePath._parse_args().
+os.PathLike.register(PurePath)
+
 
 class PurePosixPath(PurePath):
     _flavour = _posix_flavour
diff --git a/Lib/test/test_pathlib.py b/Lib/test/test_pathlib.py
index fbbd448f65d..2f2ba3cbfc7 100644
--- a/Lib/test/test_pathlib.py
+++ b/Lib/test/test_pathlib.py
@@ -190,13 +190,18 @@ class _BasePurePathTest(object):
         P = self.cls
         p = P('a')
         self.assertIsInstance(p, P)
+        class PathLike:
+            def __fspath__(self):
+                return "a/b/c"
         P('a', 'b', 'c')
         P('/a', 'b', 'c')
         P('a/b/c')
         P('/a/b/c')
+        P(PathLike())
         self.assertEqual(P(P('a')), P('a'))
         self.assertEqual(P(P('a'), 'b'), P('a/b'))
         self.assertEqual(P(P('a'), P('b')), P('a/b'))
+        self.assertEqual(P(P('a'), P('b'), P('c')), P(PathLike()))
 
     def _check_str_subclass(self, *args):
         # Issue #21127: it should be possible to construct a PurePath object
@@ -384,6 +389,12 @@ class _BasePurePathTest(object):
         parts = p.parts
         self.assertEqual(parts, (sep, 'a', 'b'))
 
+    def test_fspath_common(self):
+        P = self.cls
+        p = P('a/b')
+        self._check_str(p.__fspath__(), ('a/b',))
+        self._check_str(os.fspath(p), ('a/b',))
+
     def test_equivalences(self):
         for k, tuples in self.equivalences.items():
             canon = k.replace('/', self.sep)