gh-151416: Don't mask non-TypeError argv conversion errors in os.spawnv

os.spawnv() replaced any error raised during argv item conversion,
such as MemoryError, codec errors, or the embedded-null ValueError,
with a generic TypeError.  Only add the contextual message when the
conversion actually raised TypeError, matching how os.spawnve() and
the exec functions propagate these errors.

The test is gated to the native C spawnv: the Python fallback used
elsewhere reports conversion failures from the forked child as exit
status 127 instead of raising.

Author: gpshead

Lib/test/test_os/test_os.py

@@ -86,6 +86,15 @@ def requires_os_func(name):
     return unittest.skipUnless(hasattr(os, name), 'requires os.%s' % name)
 
 
+# On platforms without a native spawnv(), os.py provides a Python fallback
+# built on fork()+exec*() that reports argument conversion failures from the
+# child as exit status 127 instead of raising, so tests of the C
+# implementation's error paths cannot run against it.
+requires_native_spawnv = unittest.skipUnless(
+    isinstance(getattr(os, 'spawnv', None), types.BuiltinFunctionType),
+    'requires the native C os.spawnv')
+
+
 # bpo-41625: On AIX, splice() only works with a socket, not with a pipe.
 requires_splice_pipe = unittest.skipIf(sys.platform.startswith("aix"),
                                        'on AIX, splice() only accepts sockets')
@@ -3502,6 +3511,25 @@ def test_spawnve_noargs(self):
         self.assertRaises(ValueError, os.spawnve, os.P_NOWAIT, program, ('',), {})
         self.assertRaises(ValueError, os.spawnve, os.P_NOWAIT, program, [''], {})
 
+    @requires_native_spawnv
+    def test_spawnv_arg_conversion_errors(self):
+        # A non-path argv item gets a TypeError naming the argument...
+        with self.assertRaisesRegex(TypeError, 'must contain only strings'):
+            os.spawnv(os.P_NOWAIT, sys.executable, [sys.executable, 123])
+        # ...but other conversion errors must not be masked as TypeError
+        # (gh-151416).
+        with self.assertRaises(ValueError):
+            os.spawnv(os.P_NOWAIT, sys.executable,
+                      [sys.executable, 'embedded\0null'])
+
+        class RaisingPath:
+            def __fspath__(self):
+                raise RuntimeError('gotcha')
+
+        with self.assertRaisesRegex(RuntimeError, 'gotcha'):
+            os.spawnv(os.P_NOWAIT, sys.executable,
+                      [sys.executable, RaisingPath()])
+
     def _test_invalid_env(self, spawn):
         program = sys.executable
         args = self.quote_args([program, '-c', 'pass'])

Misc/NEWS.d/next/Library/2026-06-12-00-00-00.gh-issue-151416.spawnUA.rst

@@ -1,3 +1,5 @@
 Fix a crash in :func:`os.spawnv` and :func:`os.spawnve` when an *argv*
 item's :meth:`~os.PathLike.__fspath__` method mutates the *argv* list
-during argument conversion.
+during argument conversion.  :func:`!os.spawnv` argument conversion errors
+other than :exc:`TypeError`, such as the :exc:`ValueError` for an embedded
+null, are no longer replaced with a generic :exc:`TypeError`.

Modules/posixmodule.c

@@ -8230,9 +8230,14 @@ os_spawnv_impl(PyObject *module, int mode, path_t *path, PyObject *argv)
         if (!fsconvert_strdup(item, &argvlist[i])) {
             Py_DECREF(item);
             free_string_array(argvlist, i);
-            PyErr_SetString(
-                PyExc_TypeError,
-                "spawnv() arg 2 must contain only strings");
+            // Add argument context to the converter's terse TypeError, but
+            // let MemoryError, codec errors, embedded-null ValueError, etc.
+            // propagate unmasked.
+            if (PyErr_ExceptionMatches(PyExc_TypeError)) {
+                PyErr_SetString(
+                    PyExc_TypeError,
+                    "spawnv() arg 2 must contain only strings");
+            }
             return NULL;
         }
         Py_DECREF(item);