bpo-31471: Fix assertion failure in subprocess.Popen() on Windows, in case env has a bad keys() method. (python#3580)

Author: orenmn

Lib/test/test_subprocess.py

@@ -2742,6 +2742,15 @@ def test_invalid_args(self):
                           stdout=subprocess.PIPE,
                           close_fds=True)
 
+    @support.cpython_only
+    def test_issue31471(self):
+        # There shouldn't be an assertion failure in Popen() in case the env
+        # argument has a bad keys() method.
+        class BadEnv(dict):
+            keys = None
+        with self.assertRaises(TypeError):
+            subprocess.Popen([sys.executable, "-c", "pass"], env=BadEnv())
+
     def test_close_fds(self):
         # close file descriptors
         rc = subprocess.call([sys.executable, "-c",

Misc/NEWS.d/next/Core and Builtins/2017-09-14-19-47-57.bpo-31471.0yiA5Q.rst

@@ -0,0 +1,2 @@
+Fix an assertion failure in `subprocess.Popen()` on Windows, in case the env
+argument has a bad keys() method. Patch by Oren Milman.

Modules/_winapi.c

@@ -723,9 +723,13 @@ getenvironment(PyObject* environment)
     }
 
     keys = PyMapping_Keys(environment);
+    if (!keys) {
+        return NULL;
+    }
     values = PyMapping_Values(environment);
-    if (!keys || !values)
+    if (!values) {
         goto error;
+    }
 
     envsize = PySequence_Fast_GET_SIZE(keys);
     if (PySequence_Fast_GET_SIZE(values) != envsize) {