issue27186: add PathLike ABC

Lib/os.py

@@ -22,7 +22,7 @@ and opendir), and leave all pathname manipulation to os.path
 """
 
 #'
-
+import abc
 import sys, errno
 import stat as st
 
@@ -1125,3 +1125,18 @@ if not _exists('fspath'):
 
             raise TypeError("expected str, bytes or os.PathLike object, not "
                             + path_type.__name__)
+
+class PathLike(abc.ABC):
+    """
+    Abstract base class for implementing the file system path protocol.
+    """
+    @abc.abstractmethod
+    def __fspath__(self):
+        """
+        Return the file system path representation of the object.
+        """
+        raise NotImplementedError
+
+    @classmethod
+    def __subclasshook__(cls, subclass):
+        return hasattr(subclass, '__fspath__')

Lib/test/test_os.py

@@ -3127,6 +3127,8 @@ class TestPEP519(unittest.TestCase):
                 return '#feelthegil'
 
         self.assertEqual('#feelthegil', os.fspath(PathLike()))
+        self.assertTrue(issubclass(PathLike, os.PathLike))
+        self.assertTrue(isinstance(PathLike(), os.PathLike))
 
     def test_garbage_in_exception_out(self):
         vapor = type('blah', (), {})