[3.9] bpo-43219: shutil.copyfile, raise a less confusing exception instead of IsADirectoryError (GH-27049) (GH-27082)

Fixes the misleading IsADirectoryError to be FileNotFoundError.
(cherry picked from commit 248173cc04)


Co-authored-by: andrei kulakov <andrei.avk@gmail.com>

Automerge-Triggered-By: GH:gpshead

Lib/shutil.py

@@ -261,6 +261,7 @@ def copyfile(src, dst, *, follow_symlinks=True):
     if not follow_symlinks and _islink(src):
         os.symlink(os.readlink(src), dst)
     else:
+        try:
             with open(src, 'rb') as fsrc, open(dst, 'wb') as fdst:
                 # macOS
                 if _HAS_FCOPYFILE:
@@ -284,6 +285,13 @@ def copyfile(src, dst, *, follow_symlinks=True):
 
                 copyfileobj(fsrc, fdst)
 
+        # Issue 43219, raise a less confusing exception
+        except IsADirectoryError as e:
+            if os.path.exists(dst):
+                raise
+            else:
+                raise FileNotFoundError(f'Directory does not exist: {dst}') from e
+
     return dst
 
 def copymode(src, dst, *, follow_symlinks=True):

Lib/test/test_shutil.py

@@ -1243,6 +1243,15 @@ def test_copyfile_same_file(self):
         # Make sure file is not corrupted.
         self.assertEqual(read_file(src_file), 'foo')
 
+    @unittest.skipIf(MACOS or _winapi, 'On MACOS and Windows the errors are not confusing (though different)')
+    def test_copyfile_nonexistent_dir(self):
+        # Issue 43219
+        src_dir = self.mkdtemp()
+        src_file = os.path.join(src_dir, 'foo')
+        dst = os.path.join(src_dir, 'does_not_exist/')
+        write_file(src_file, 'foo')
+        self.assertRaises(FileNotFoundError, shutil.copyfile, src_file, dst)
+
 
 class TestArchives(BaseTest, unittest.TestCase):
 

Misc/NEWS.d/next/Library/2021-07-09-07-14-37.bpo-41928.Q1jMrr.rst

@@ -0,0 +1,4 @@
+Update :func:`shutil.copyfile` to raise :exc:`FileNotFoundError` instead of
+confusing :exc:`IsADirectoryError` when a path ending with a
+:const:`os.path.sep` does not exist; :func:`shutil.copy` and
+:func:`shutil.copy2` are also affected.