bpo-24744: Raises error in pkgutil.walk_packages if path is str (#1926)

bpo-24744: Raise error in pkgutil.walk_packages if path is str

Previously an empty result list was accidentallly returned, since the
code iterated over the string as if it were the expected list of paths,
and of course found nothing.

Doc/whatsnew/3.7.rst

@@ -395,6 +395,10 @@ that may require changes to your code.
 Changes in the Python API
 -------------------------
 
+* :meth:`pkgutil.walk_packages` now raises ValueError if *path* is a string.
+  Previously an empty list was returned. (Contributed by Sanyam Khurana in
+  :issue:`24744`.)
+
 * A format string argument for :meth:`string.Formatter.format`
   is now :ref:`positional-only <positional-only_parameter>`.
   Passing it as a keyword argument was deprecated in Python 3.5. (Contributed

Lib/pkgutil.py

@@ -119,6 +119,9 @@ def iter_modules(path=None, prefix=''):
     """
     if path is None:
         importers = iter_importers()
+    elif isinstance(path, str):
+        raise ValueError("path must be None or list of paths to look for "
+                        "modules in")
     else:
         importers = map(get_importer, path)
 

Lib/test/test_pkgutil.py

@@ -176,6 +176,15 @@ class PkgutilTests(unittest.TestCase):
                 continue
             del sys.modules[pkg]
 
+    def test_walk_packages_raises_on_string_or_bytes_input(self):
+
+        str_input = 'test_dir'
+        with self.assertRaises((TypeError, ValueError)):
+            list(pkgutil.walk_packages(str_input))
+
+        bytes_input = b'test_dir'
+        with self.assertRaises((TypeError, ValueError)):
+            list(pkgutil.walk_packages(bytes_input))
 
 
 class PkgutilPEP302Tests(unittest.TestCase):

Misc/NEWS

@@ -362,6 +362,9 @@ Extension Modules
 Library
 -------
 
+- bpo-24744: pkgutil.walk_packages function now raises ValueError if *path*
+  is a string. Patch by Sanyam Khurana.
+
 - bpo-24484: Avoid race condition in multiprocessing cleanup.
 
 - bpo-30589: Fix multiprocessing.Process.exitcode to return the opposite