bpo-18283: Add support for bytes to shutil.which

Doc/library/shutil.rst

@@ -396,6 +396,9 @@ Directory and files operations
 
    .. versionadded:: 3.3
 
+   .. versionchanged:: 3.8
+      The :class:`bytes` type is now accepted.  If *cmd* type is
+      :class:`bytes`, the result type is also :class:`bytes`.
 
 .. exception:: Error
 

Lib/shutil.py

@@ -1279,6 +1279,15 @@ def get_terminal_size(fallback=(80, 24)):
 
     return os.terminal_size((columns, lines))
 
+
+# Check that a given file can be accessed with the correct mode.
+# Additionally check that `file` is not a directory, as on Windows
+# directories pass the os.access check.
+def _access_check(fn, mode):
+    return (os.path.exists(fn) and os.access(fn, mode)
+            and not os.path.isdir(fn))
+
+
 def which(cmd, mode=os.F_OK | os.X_OK, path=None):
     """Given a command, mode, and a PATH string, return the path which
     conforms to the given mode on the PATH, or None if there is no such
@@ -1289,13 +1298,6 @@ def which(cmd, mode=os.F_OK | os.X_OK, path=None):
     path.
 
     """
-    # Check that a given file can be accessed with the correct mode.
-    # Additionally check that `file` is not a directory, as on Windows
-    # directories pass the os.access check.
-    def _access_check(fn, mode):
-        return (os.path.exists(fn) and os.access(fn, mode)
-                and not os.path.isdir(fn))
-
     # If we're given a path with a directory part, look it up directly rather
     # than referring to PATH directories. This includes checking relative to the
     # current directory, e.g. ./script
@@ -1304,19 +1306,31 @@ def _access_check(fn, mode):
             return cmd
         return None
 
+    use_bytes = isinstance(cmd, bytes)
+
     if path is None:
         path = os.environ.get("PATH", os.defpath)
     if not path:
         return None
-    path = path.split(os.pathsep)
+    if use_bytes:
+        path = os.fsencode(path)
+        path = path.split(os.fsencode(os.pathsep))
+    else:
+        path = os.fsdecode(path)
+        path = path.split(os.pathsep)
 
     if sys.platform == "win32":
         # The current directory takes precedence on Windows.
-        if not os.curdir in path:
-            path.insert(0, os.curdir)
+        curdir = os.curdir
+        if use_bytes:
+            curdir = os.fsencode(curdir)
+        if curdir not in path:
+            path.insert(0, curdir)
 
         # PATHEXT is necessary to check on Windows.
         pathext = os.environ.get("PATHEXT", "").split(os.pathsep)
+        if use_bytes:
+            pathext = [os.fsencode(ext) for ext in pathext]
         # See if the given file matches any of the expected path extensions.
         # This will allow us to short circuit when given "python.exe".
         # If it does match, only test that one, otherwise we have to try

Lib/test/test_shutil.py

@@ -1517,6 +1517,9 @@ def setUp(self):
         os.chmod(self.temp_file.name, stat.S_IXUSR)
         self.addCleanup(self.temp_file.close)
         self.dir, self.file = os.path.split(self.temp_file.name)
+        self.env_path = self.dir
+        self.curdir = os.curdir
+        self.ext = ".EXE"
 
     def test_basic(self):
         # Given an EXE in a directory, it should be returned.
@@ -1549,7 +1552,7 @@ def test_cwd(self):
             rv = shutil.which(self.file, path=base_dir)
             if sys.platform == "win32":
                 # Windows: current directory implicitly on PATH
-                self.assertEqual(rv, os.path.join(os.curdir, self.file))
+                self.assertEqual(rv, os.path.join(self.curdir, self.file))
             else:
                 # Other platforms: shouldn't match in the current directory.
                 self.assertIsNone(rv)
@@ -1581,19 +1584,19 @@ def test_pathext_checking(self):
         # Ask for the file without the ".exe" extension, then ensure that
         # it gets found properly with the extension.
         rv = shutil.which(self.file[:-4], path=self.dir)
-        self.assertEqual(rv, self.temp_file.name[:-4] + ".EXE")
+        self.assertEqual(rv, self.temp_file.name[:-4] + self.ext)
 
     def test_environ_path(self):
         with support.EnvironmentVarGuard() as env:
-            env['PATH'] = self.dir
+            env['PATH'] = self.env_path
             rv = shutil.which(self.file)
             self.assertEqual(rv, self.temp_file.name)
 
     def test_empty_path(self):
         base_dir = os.path.dirname(self.dir)
         with support.change_cwd(path=self.dir), \
              support.EnvironmentVarGuard() as env:
-            env['PATH'] = self.dir
+            env['PATH'] = self.env_path
             rv = shutil.which(self.file, path='')
             self.assertIsNone(rv)
 
@@ -1604,6 +1607,16 @@ def test_empty_path_no_PATH(self):
             self.assertIsNone(rv)
 
 
+class TestWhichBytes(TestWhich):
+    def setUp(self):
+        TestWhich.setUp(self)
+        self.dir = os.fsencode(self.dir)
+        self.file = os.fsencode(self.file)
+        self.temp_file.name = os.fsencode(self.temp_file.name)
+        self.curdir = os.fsencode(self.curdir)
+        self.ext = os.fsencode(self.ext)
+
+
 class TestMove(unittest.TestCase):
 
     def setUp(self):

Misc/NEWS.d/next/Library/2019-02-11-09-24-08.bpo-18283.BT3Jhc.rst

@@ -0,0 +1 @@
+Add support for bytes to :func:`shutil.which`.