fix PYTHONWARNINGS handling to not modify the original env value and improve

its tests

Lib/test/test_warnings.py

@@ -683,7 +683,8 @@ class EnvironmentVariableTests(BaseTest):
         p = subprocess.Popen([sys.executable,
                 "-c", "import sys; sys.stdout.write(str(sys.warnoptions))"],
                 stdout=subprocess.PIPE, env=newenv)
-        self.assertEqual(p.stdout.read(), "['ignore::DeprecationWarning']")
+        self.assertEqual(p.communicate()[0], "['ignore::DeprecationWarning']")
+        self.assertEqual(p.wait(), 0)
 
     def test_comma_separated_warnings(self):
         newenv = os.environ.copy()
@@ -692,8 +693,9 @@ class EnvironmentVariableTests(BaseTest):
         p = subprocess.Popen([sys.executable,
                 "-c", "import sys; sys.stdout.write(str(sys.warnoptions))"],
                 stdout=subprocess.PIPE, env=newenv)
-        self.assertEqual(p.stdout.read(),
+        self.assertEqual(p.communicate()[0],
                 "['ignore::DeprecationWarning', 'ignore::UnicodeWarning']")
+        self.assertEqual(p.wait(), 0)
 
     def test_envvar_and_command_line(self):
         newenv = os.environ.copy()
@@ -701,8 +703,9 @@ class EnvironmentVariableTests(BaseTest):
         p = subprocess.Popen([sys.executable, "-W" "ignore::UnicodeWarning",
                 "-c", "import sys; sys.stdout.write(str(sys.warnoptions))"],
                 stdout=subprocess.PIPE, env=newenv)
-        self.assertEqual(p.stdout.read(),
+        self.assertEqual(p.communicate()[0],
                 "['ignore::UnicodeWarning', 'ignore::DeprecationWarning']")
+        self.assertEqual(p.wait(), 0)
 
 class CEnvironmentVariableTests(EnvironmentVariableTests):
     module = c_warnings

Modules/main.c

@@ -421,14 +421,19 @@ Py_Main(int argc, char **argv)
 	    (p = Py_GETENV("PYTHONNOUSERSITE")) && *p != '\0')
 		Py_NoUserSiteDirectory = 1;
 
-	if ((p = Py_GETENV("PYTHONWARNINGS")) && *p != '\0')
-	{
-		char* warning = strtok(p, ",");
-		while (warning != NULL)
-		{
+	if ((p = Py_GETENV("PYTHONWARNINGS")) && *p != '\0') {
+		char *buf, *warning;
+
+		buf = (char *)malloc(strlen(p) + 1);
+		if (buf == NULL)
+			Py_FatalError(
+			   "not enough memory to copy PYTHONWARNINGS");
+		strcpy(buf, p);
+		for (warning = strtok(buf, ",");
+		     warning != NULL;
+		     warning = strtok(NULL, ","))
 			PySys_AddWarnOption(warning);
-			warning = strtok(NULL, ",");
-		}
+		free(buf);
 	}
 
 	if (command == NULL && module == NULL && _PyOS_optind < argc &&