Index: Doc/library/shutil.rst
===================================================================
--- Doc/library/shutil.rst	(revision 76432)
+++ Doc/library/shutil.rst	(working copy)
@@ -161,6 +161,16 @@
    .. versionadded:: 2.3
 
 
+.. function:: which(file [, mode=os.F_OK | os.X_OK[, path=None]])
+
+   Return a generator which yields full paths in which the *file* name exists
+   in a directory on *path* and has the given *mode*. By default, *mode*
+   matches an inclusive OR of os.F_OK and os.X_OK - an existing executable file.
+   The *path* is, by default, the ``PATH`` variable on the platform, or the
+   string passed in as *path*. In the event that a ``PATH`` variable is not
+   found, :const:`os.defpath` is used.
+
+
 .. exception:: Error
 
    This exception collects exceptions that raised during a multi-file operation. For
@@ -237,4 +247,3 @@
        return []   # nothing will be ignored
 
    copytree(source, destination, ignore=_logpath)
-
Index: Lib/shutil.py
===================================================================
--- Lib/shutil.py	(revision 76432)
+++ Lib/shutil.py	(working copy)
@@ -278,6 +278,19 @@
             copy2(src, real_dst)
             os.unlink(src)
 
+def which(file, mode=os.F_OK | os.X_OK, path=None):
+	"""Locate a file in the user's path, or a supplied path. The function
+	yields full paths in which the given file matches a file in a directory on
+	the path.
+	"""
+	if not path:
+		path = os.environ.get("PATH", os.defpath)
+
+	for dir in path.split(os.pathsep):
+		full_path = os.path.join(dir, file)
+		if os.path.exists(full_path) and os.access(full_path, mode):
+			yield full_path
+
 def _destinsrc(src, dst):
     src = abspath(src)
     dst = abspath(dst)
Index: Lib/test/test_shutil.py
===================================================================
--- Lib/test/test_shutil.py	(revision 76432)
+++ Lib/test/test_shutil.py	(working copy)
@@ -277,7 +277,29 @@
                 shutil.rmtree(TESTFN, ignore_errors=True)
                 shutil.rmtree(TESTFN2, ignore_errors=True)
 
+    def test_which(self):
+        temp_dir = tempfile.mkdtemp()
+        temp_file = tempfile.NamedTemporaryFile(prefix="test")
+        dir, file = os.path.split(temp_file.name)
 
+        os.chmod(temp_file.name, stat.S_IXUSR)
+        files = shutil.which(file, path=dir)
+        self.assertEqual(list(files), [temp_file.name])
+
+        os.chmod(temp_file.name, os.R_OK)
+        files = shutil.which(file, path=dir)
+        # The default mask shouldn't match this file
+        self.assertEqual(list(files), [])
+
+        files = shutil.which(file, mode=shutil.stat.S_IRUSR, path=dir)
+        # The given mask should match this file
+        self.assertEqual(list(files), [temp_file.name])
+
+        files = shutil.which("foo", path=dir)
+        # `foo` should'nt exist in `dir`
+        self.assertEqual(list(files), [])
+
+
 class TestMove(unittest.TestCase):
 
     def setUp(self):