bpo-32101: Add PYTHONDEVMODE environment variable (#4624)

* bpo-32101: Add sys.flags.dev_mode flag
  Rename also the "Developer mode" to the "Development mode".
* bpo-32101: Add PYTHONDEVMODE environment variable
  Mention it in the development chapiter.

Doc/library/development.rst

@@ -24,3 +24,6 @@ The list of modules described in this chapter is:
    unittest.mock-examples.rst
    2to3.rst
    test.rst
+
+See also the Python development mode: the :option:`-X` ``dev`` option and
+:envvar:`PYTHONDEVMODE` environment variable.

Doc/library/sys.rst

@@ -334,6 +334,7 @@ always available.
    :const:`bytes_warning`        :option:`-b`
    :const:`quiet`                :option:`-q`
    :const:`hash_randomization`   :option:`-R`
+   :const:`dev_mode`             :option:`-X` ``dev``
    ============================= =============================
 
    .. versionchanged:: 3.2
@@ -345,6 +346,9 @@ always available.
    .. versionchanged:: 3.3
       Removed obsolete ``division_warning`` attribute.
 
+   .. versionchanged:: 3.7
+      Added ``dev_mode`` attribute for the new :option:`-X` ``dev`` flag.
+
 
 .. data:: float_info
 

Doc/using/cmdline.rst

@@ -411,7 +411,7 @@ Miscellaneous options
      nested imports).  Note that its output may be broken in multi-threaded
      application.  Typical usage is ``python3 -X importtime -c 'import
      asyncio'``.  See also :envvar:`PYTHONPROFILEIMPORTTIME`.
-   * ``-X dev``: enable CPython's "developer mode", introducing additional
+   * ``-X dev``: enable CPython's "development mode", introducing additional
      runtime checks which are too expensive to be enabled by default. It should
      not be more verbose than the default if the code is correct: new warnings
      are only emitted when an issue is detected. Effect of the developer mode:
@@ -426,6 +426,8 @@ Miscellaneous options
      * Enable the :mod:`faulthandler` module to dump the Python traceback
        on a crash.
      * Enable :ref:`asyncio debug mode <asyncio-debug-mode>`.
+     * Set the :attr:`~sys.flags.dev_mode` attribute of :attr:`sys.flags` to
+       ``True``
 
    It also allows passing arbitrary values and retrieving them through the
    :data:`sys._xoptions` dictionary.
@@ -796,6 +798,14 @@ conflict.
    .. versionadded:: 3.7
       See :pep:`538` for more details.
 
+
+.. envvar:: PYTHONDEVMODE
+
+   If this environment variable is set to a non-empty string, enable the
+   CPython "development mode". See the :option:`-X` ``dev`` option.
+
+   .. versionadded:: 3.7
+
 Debug-mode variables
 ~~~~~~~~~~~~~~~~~~~~
 

Doc/whatsnew/3.7.rst

@@ -185,10 +185,10 @@ resolution on Linux and Windows.
        PEP written and implemented by Victor Stinner
 
 
-New Developer Mode: -X dev
---------------------------
+New Development Mode: -X dev
+----------------------------
 
-Add a new "developer mode": ``-X dev`` command line option to enable debug
+Add a new "development mode": ``-X dev`` command line option to enable debug
 checks at runtime.
 
 In short, ``python3 -X dev ...`` behaves as ``PYTHONMALLOC=debug python3 -W
@@ -371,6 +371,11 @@ string
 expression pattern for braced placeholders and non-braced placeholders
 separately.  (Contributed by Barry Warsaw in :issue:`1198569`.)
 
+sys
+---
+
+Added :attr:`sys.flags.dev_mode` flag for the new development mode.
+
 time
 ----
 

Lib/asyncio/coroutines.py

@@ -27,11 +27,9 @@ def _is_debug_mode():
     # before you define your coroutines.  A downside of using this feature
     # is that tracebacks show entries for the CoroWrapper.__next__ method
     # when _DEBUG is true.
-    debug = (not sys.flags.ignore_environment and
-             bool(os.environ.get('PYTHONASYNCIODEBUG')))
-    if hasattr(sys, '_xoptions') and 'dev' in sys._xoptions:
-        debug = True
-    return debug
+    return (sys.flags.dev_mode
+            or (not sys.flags.ignore_environment
+                and bool(os.environ.get('PYTHONASYNCIODEBUG'))))
 
 
 _DEBUG = _is_debug_mode()

Lib/test/test_cmd_line.py

@@ -508,14 +508,18 @@ def test_sys_flags_set(self):
             with self.subTest(envar_value=value):
                 assert_python_ok('-c', code, **env_vars)
 
-    def run_xdev(self, *args, check_exitcode=True):
+    def run_xdev(self, *args, check_exitcode=True, xdev=True):
         env = dict(os.environ)
         env.pop('PYTHONWARNINGS', None)
+        env.pop('PYTHONDEVMODE', None)
         # Force malloc() to disable the debug hooks which are enabled
         # by default for Python compiled in debug mode
         env['PYTHONMALLOC'] = 'malloc'
 
-        args = (sys.executable, '-X', 'dev', *args)
+        if xdev:
+            args = (sys.executable, '-X', 'dev', *args)
+        else:
+            args = (sys.executable, *args)
         proc = subprocess.run(args,
                               stdout=subprocess.PIPE,
                               stderr=subprocess.STDOUT,
@@ -526,6 +530,14 @@ def run_xdev(self, *args, check_exitcode=True):
         return proc.stdout.rstrip()
 
     def test_xdev(self):
+        # sys.flags.dev_mode
+        code = "import sys; print(sys.flags.dev_mode)"
+        out = self.run_xdev("-c", code, xdev=False)
+        self.assertEqual(out, "False")
+        out = self.run_xdev("-c", code)
+        self.assertEqual(out, "True")
+
+        # Warnings
         code = ("import sys, warnings; "
                 "print(' '.join('%s::%s' % (f[0], f[2].__name__) "
                                 "for f in warnings.filters))")
@@ -555,6 +567,7 @@ def test_xdev(self):
                          "default::ResourceWarning "
                          "default::Warning")
 
+        # Memory allocator debug hooks
         try:
             import _testcapi
         except ImportError:
@@ -569,6 +582,7 @@ def test_xdev(self):
                 alloc_name = "malloc_debug"
             self.assertEqual(out, alloc_name)
 
+        # Faulthandler
         try:
             import faulthandler
         except ImportError:
@@ -581,6 +595,7 @@ def test_xdev(self):
     def check_pythonmalloc(self, env_var, name):
         code = 'import _testcapi; print(_testcapi.pymem_getallocatorsname())'
         env = dict(os.environ)
+        env.pop('PYTHONDEVMODE', None)
         if env_var is not None:
             env['PYTHONMALLOC'] = env_var
         else:
@@ -621,6 +636,24 @@ def test_pythonmalloc(self):
             with self.subTest(env_var=env_var, name=name):
                 self.check_pythonmalloc(env_var, name)
 
+    def test_pythondevmode_env(self):
+        # Test the PYTHONDEVMODE environment variable
+        code = "import sys; print(sys.flags.dev_mode)"
+        env = dict(os.environ)
+        env.pop('PYTHONDEVMODE', None)
+        args = (sys.executable, '-c', code)
+
+        proc = subprocess.run(args, stdout=subprocess.PIPE,
+                              universal_newlines=True, env=env)
+        self.assertEqual(proc.stdout.rstrip(), 'False')
+        self.assertEqual(proc.returncode, 0, proc)
+
+        env['PYTHONDEVMODE'] = '1'
+        proc = subprocess.run(args, stdout=subprocess.PIPE,
+                              universal_newlines=True, env=env)
+        self.assertEqual(proc.stdout.rstrip(), 'True')
+        self.assertEqual(proc.returncode, 0, proc)
+
 
 class IgnoreEnvironmentTest(unittest.TestCase):
 

Lib/test/test_sys.py

@@ -526,10 +526,12 @@ def test_sys_flags(self):
         attrs = ("debug",
                  "inspect", "interactive", "optimize", "dont_write_bytecode",
                  "no_user_site", "no_site", "ignore_environment", "verbose",
-                 "bytes_warning", "quiet", "hash_randomization", "isolated")
+                 "bytes_warning", "quiet", "hash_randomization", "isolated",
+                 "dev_mode")
         for attr in attrs:
             self.assertTrue(hasattr(sys.flags, attr), attr)
-            self.assertEqual(type(getattr(sys.flags, attr)), int, attr)
+            attr_type = bool if attr == "dev_mode" else int
+            self.assertEqual(type(getattr(sys.flags, attr)), attr_type, attr)
         self.assertTrue(repr(sys.flags))
         self.assertEqual(len(sys.flags), len(attrs))
 

Misc/NEWS.d/next/Library/2017-11-29-00-42-47.bpo-321010.-axD5l.rst

@@ -0,0 +1 @@
+Add :attr:`sys.flags.dev_mode` flag

Modules/main.c

@@ -124,7 +124,8 @@ static const char usage_6[] =
 "   hooks.\n"
 "PYTHONCOERCECLOCALE: if this variable is set to 0, it disables the locale\n"
 "   coercion behavior. Use PYTHONCOERCECLOCALE=warn to request display of\n"
-"   locale coercion and locale compatibility warnings on stderr.\n";
+"   locale coercion and locale compatibility warnings on stderr.\n"
+"PYTHONDEVMODE: enable the development mode.\n";
 
 static void
 pymain_usage(int error, const wchar_t* program)
@@ -1520,7 +1521,9 @@ pymain_parse_envvars(_PyMain *pymain)
     if (pymain_init_tracemalloc(pymain) < 0) {
         return -1;
     }
-    if (pymain_get_xoption(pymain, L"dev")) {
+    if (pymain_get_xoption(pymain, L"dev" ) ||
+        pymain_get_env_var("PYTHONDEVMODE"))
+    {
         core_config->dev_mode = 1;
         core_config->faulthandler = 1;
         core_config->allocator = "debug";

Python/sysmodule.c

@@ -1814,21 +1814,23 @@ static PyStructSequence_Field flags_fields[] = {
     {"quiet",                   "-q"},
     {"hash_randomization",      "-R"},
     {"isolated",                "-I"},
+    {"dev_mode",                "-X dev"},
     {0}
 };
 
 static PyStructSequence_Desc flags_desc = {
     "sys.flags",        /* name */
     flags__doc__,       /* doc */
     flags_fields,       /* fields */
-    13
+    14
 };
 
 static PyObject*
 make_flags(void)
 {
     int pos = 0;
     PyObject *seq;
+    _PyCoreConfig *core_config = &_PyGILState_GetInterpreterStateUnsafe()->core_config;
 
     seq = PyStructSequence_New(&FlagsType);
     if (seq == NULL)
@@ -1853,6 +1855,7 @@ make_flags(void)
     SetFlag(Py_HashRandomizationFlag);
     SetFlag(Py_IsolatedFlag);
 #undef SetFlag
+    PyStructSequence_SET_ITEM(seq, pos++, PyBool_FromLong(core_config->dev_mode));
 
     if (PyErr_Occurred()) {
         Py_DECREF(seq);