I'm only backporting the tests (which run fine), as well as

a shortened version of Lib/test/script_helper.py.

Merged revisions 86395 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/branches/py3k

........
  r86395 | antoine.pitrou | 2010-11-10 14:55:25 +0100 (mer., 10 nov. 2010) | 4 lines

  Issue #10372: Import the warnings module only after the IO library is
  initialized, so as to avoid bootstrap issues with the '-W' option.
........

Lib/test/script_helper.py

+# Common utility functions used by various script execution tests
+#  e.g. test_cmd_line, test_cmd_line_script and test_runpy
+
+import sys
+import os
+import os.path
+import tempfile
+import subprocess
+import py_compile
+import contextlib
+import shutil
+import zipfile
+
+
+# Executing the interpreter in a subprocess
+def _assert_python(expected_success, *args, **env_vars):
+    cmd_line = [sys.executable]
+    if not env_vars:
+        cmd_line.append('-E')
+    cmd_line.extend(args)
+    # Need to preserve the original environment, for in-place testing of
+    # shared library builds.
+    env = os.environ.copy()
+    env.update(env_vars)
+    p = subprocess.Popen(cmd_line, stdin=subprocess.PIPE,
+                         stdout=subprocess.PIPE, stderr=subprocess.PIPE,
+                         env=env)
+    try:
+        out, err = p.communicate()
+    finally:
+        subprocess._cleanup()
+        p.stdout.close()
+        p.stderr.close()
+    rc = p.returncode
+    if (rc and expected_success) or (not rc and not expected_success):
+        raise AssertionError(
+            "Process return code is %d, "
+            "stderr follows:\n%s" % (rc, err.decode('ascii', 'ignore')))
+    return rc, out, err
+
+def assert_python_ok(*args, **env_vars):
+    """
+    Assert that running the interpreter with `args` and optional environment
+    variables `env_vars` is ok and return a (return code, stdout, stderr) tuple.
+    """
+    return _assert_python(True, *args, **env_vars)
+
+def assert_python_failure(*args, **env_vars):
+    """
+    Assert that running the interpreter with `args` and optional environment
+    variables `env_vars` fails and return a (return code, stdout, stderr) tuple.
+    """
+    return _assert_python(False, *args, **env_vars)
+
+def spawn_python(*args):
+    cmd_line = [sys.executable, '-E']
+    cmd_line.extend(args)
+    return subprocess.Popen(cmd_line, stdin=subprocess.PIPE,
+                            stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+
+def kill_python(p):
+    p.stdin.close()
+    data = p.stdout.read()
+    p.stdout.close()
+    # try to cleanup the child so we don't appear to leak when running
+    # with regrtest -R.
+    p.wait()
+    subprocess._cleanup()
+    return data
+
+# Script creation utilities
+@contextlib.contextmanager
+def temp_dir():
+    dirname = tempfile.mkdtemp()
+    dirname = os.path.realpath(dirname)
+    try:
+        yield dirname
+    finally:
+        shutil.rmtree(dirname)
+
+def make_script(script_dir, script_basename, source):
+    script_filename = script_basename+os.extsep+'py'
+    script_name = os.path.join(script_dir, script_filename)
+    # The script should be encoded to UTF-8, the default string encoding
+    script_file = open(script_name, 'w', encoding='utf-8')
+    script_file.write(source)
+    script_file.close()
+    return script_name
+
+def make_pkg(pkg_dir, init_source=''):
+    os.mkdir(pkg_dir)
+    make_script(pkg_dir, '__init__', init_source)
+
+def make_zip_pkg(zip_dir, zip_basename, pkg_name, script_basename,
+                 source, depth=1, compiled=False):
+    unlink = []
+    init_name = make_script(zip_dir, '__init__', '')
+    unlink.append(init_name)
+    init_basename = os.path.basename(init_name)
+    script_name = make_script(zip_dir, script_basename, source)
+    unlink.append(script_name)
+    if compiled:
+        init_name = py_compile(init_name, doraise=True)
+        script_name = py_compile(script_name, doraise=True)
+        unlink.extend((init_name, script_name))
+    pkg_names = [os.sep.join([pkg_name]*i) for i in range(1, depth+1)]
+    script_name_in_zip = os.path.join(pkg_names[-1], os.path.basename(script_name))
+    zip_filename = zip_basename+os.extsep+'zip'
+    zip_name = os.path.join(zip_dir, zip_filename)
+    zip_file = zipfile.ZipFile(zip_name, 'w')
+    for name in pkg_names:
+        init_name_in_zip = os.path.join(name, init_basename)
+        zip_file.write(init_name, init_name_in_zip)
+    zip_file.write(script_name, script_name_in_zip)
+    zip_file.close()
+    for name in unlink:
+        os.unlink(name)
+    #if test.support.verbose:
+    #    zip_file = zipfile.ZipFile(zip_name, 'r')
+    #    print 'Contents of %r:' % zip_name
+    #    zip_file.printdir()
+    #    zip_file.close()
+    return zip_name, os.path.join(zip_name, script_name_in_zip)

Lib/test/test_warnings.py

@@ -7,6 +7,7 @@ import unittest
 import tempfile
 import subprocess
 from test import support
+from test.script_helper import assert_python_ok
 
 from test import warning_tests
 
@@ -394,6 +395,22 @@ class WCmdLineTests(unittest.TestCase):
             self.module._setoption('error::Warning::0')
             self.assertRaises(UserWarning, self.module.warn, 'convert to error')
 
+    def test_improper_option(self):
+        # Same as above, but check that the message is printed out when
+        # the interpreter is executed. This also checks that options are
+        # actually parsed at all.
+        rc, out, err = assert_python_ok("-Wxxx", "-c", "pass")
+        self.assertIn(b"Invalid -W option ignored: invalid action: 'xxx'", err)
+
+    def test_warnings_bootstrap(self):
+        # Check that the warnings module does get loaded when -W<some option>
+        # is used (see issue #10372 for an example of silent bootstrap failure).
+        rc, out, err = assert_python_ok("-Wi", "-c",
+            "import sys; sys.modules['warnings'].warn('foo', RuntimeWarning)")
+        # '-Wi' was observed
+        self.assertFalse(out.strip())
+        self.assertNotIn(b'RuntimeWarning', err)
+
 class CWCmdLineTests(BaseTest, WCmdLineTests):
     module = c_warnings
 

Misc/NEWS

@@ -10,6 +10,9 @@ What's New in Python 3.1.3?
 Core and Builtins
 -----------------
 
+- Issue #10372: Import the warnings module only after the IO library is
+  initialized, so as to avoid bootstrap issues with the '-W' option.
+
 - Issue #10221: dict.pop(k) now has a key error message that includes the
   missing key (same message d[k] returns for missing keys).