bpo-39395: putenv() and unsetenv() always available (GH-18135)

The os.putenv() and os.unsetenv() functions are now always available.

On non-Windows platforms, Python now requires setenv() and unsetenv()
functions to build.

Remove putenv_dict from posixmodule.c: it's not longer needed.

Author: vstinner

Doc/library/os.rst

@@ -111,9 +111,9 @@ process and user.
    to the environment made after this time are not reflected in ``os.environ``,
    except for changes made by modifying ``os.environ`` directly.
 
-   If the platform supports the :func:`putenv` function, this mapping may be used
-   to modify the environment as well as query the environment.  :func:`putenv` will
-   be called automatically when the mapping is modified.
+   This mapping may be used to modify the environment as well as query the
+   environment.  :func:`putenv` will be called automatically when the mapping
+   is modified.
 
    On Unix, keys and values use :func:`sys.getfilesystemencoding` and
    ``'surrogateescape'`` error handler. Use :data:`environb` if you would like
@@ -130,14 +130,10 @@ process and user.
       cause memory leaks.  Refer to the system documentation for
       :c:func:`putenv`.
 
-   If :func:`putenv` is not provided, a modified copy of this mapping  may be
-   passed to the appropriate process-creation functions to cause  child processes
-   to use a modified environment.
-
-   If the platform supports the :func:`unsetenv` function, you can delete items in
-   this mapping to unset environment variables. :func:`unsetenv` will be called
-   automatically when an item is deleted from ``os.environ``, and when
-   one of the :meth:`pop` or :meth:`clear` methods is called.
+   You can delete items in this mapping to unset environment variables.
+   :func:`unsetenv` will be called automatically when an item is deleted from
+   ``os.environ``, and when one of the :meth:`pop` or :meth:`clear` methods is
+   called.
 
 
 .. data:: environb
@@ -439,17 +435,18 @@ process and user.
    changes to the environment affect subprocesses started with :func:`os.system`,
    :func:`popen` or :func:`fork` and :func:`execv`.
 
-   .. availability:: most flavors of Unix, Windows.
+   Assignments to items in ``os.environ`` are automatically translated into
+   corresponding calls to :func:`putenv`; however, calls to :func:`putenv`
+   don't update ``os.environ``, so it is actually preferable to assign to items
+   of ``os.environ``.
 
    .. note::
 
       On some platforms, including FreeBSD and Mac OS X, setting ``environ`` may
-      cause memory leaks. Refer to the system documentation for putenv.
+      cause memory leaks. Refer to the system documentation for :c:func:`putenv`.
 
-   When :func:`putenv` is supported, assignments to items in ``os.environ`` are
-   automatically translated into corresponding calls to :func:`putenv`; however,
-   calls to :func:`putenv` don't update ``os.environ``, so it is actually
-   preferable to assign to items of ``os.environ``.
+   .. versionchanged:: 3.9
+      The function is now always available.
 
 
 .. function:: setegid(egid)
@@ -638,15 +635,13 @@ process and user.
    environment affect subprocesses started with :func:`os.system`, :func:`popen` or
    :func:`fork` and :func:`execv`.
 
-   When :func:`unsetenv` is supported, deletion of items in ``os.environ`` is
-   automatically translated into a corresponding call to :func:`unsetenv`; however,
-   calls to :func:`unsetenv` don't update ``os.environ``, so it is actually
-   preferable to delete items of ``os.environ``.
-
-   .. availability:: most flavors of Unix, Windows.
+   Deletion of items in ``os.environ`` is automatically translated into a
+   corresponding call to :func:`unsetenv`; however, calls to :func:`unsetenv`
+   don't update ``os.environ``, so it is actually preferable to delete items of
+   ``os.environ``.
 
    .. versionchanged:: 3.9
-      The function is now also available on Windows.
+      The function is now always available and is also available on Windows.
 
 
 .. _os-newstreams:

Doc/whatsnew/3.9.rst

@@ -227,6 +227,10 @@ descriptors.
 The :func:`os.unsetenv` function is now also available on Windows.
 (Contributed by Victor Stinner in :issue:`39413`.)
 
+The :func:`os.putenv` and :func:`os.unsetenv` functions are now always
+available.
+(Contributed by Victor Stinner in :issue:`39395`.)
+
 poplib
 ------
 
@@ -331,6 +335,10 @@ Build and C API Changes
   Python 3.0, it has been ignored and unused.
   (Contributed by Jeroen Demeyer in :issue:`36974`.)
 
+* On non-Windows platforms, the :c:func:`setenv` and :c:func:`unsetenv`
+  functions are now required to build Python.
+  (Contributed by Victor Stinner in :issue:`39395`.)
+
 
 Deprecated
 ==========

Lib/os.py

@@ -654,17 +654,15 @@ def get_exec_path(env=None):
     return path_list.split(pathsep)
 
 
-# Change environ to automatically call putenv(), unsetenv if they exist.
+# Change environ to automatically call putenv() and unsetenv()
 from _collections_abc import MutableMapping
 
 class _Environ(MutableMapping):
-    def __init__(self, data, encodekey, decodekey, encodevalue, decodevalue, putenv, unsetenv):
+    def __init__(self, data, encodekey, decodekey, encodevalue, decodevalue):
         self.encodekey = encodekey
         self.decodekey = decodekey
         self.encodevalue = encodevalue
         self.decodevalue = decodevalue
-        self.putenv = putenv
-        self.unsetenv = unsetenv
         self._data = data
 
     def __getitem__(self, key):
@@ -678,12 +676,12 @@ def __getitem__(self, key):
     def __setitem__(self, key, value):
         key = self.encodekey(key)
         value = self.encodevalue(value)
-        self.putenv(key, value)
+        putenv(key, value)
         self._data[key] = value
 
     def __delitem__(self, key):
         encodedkey = self.encodekey(key)
-        self.unsetenv(encodedkey)
+        unsetenv(encodedkey)
         try:
             del self._data[encodedkey]
         except KeyError:
@@ -712,22 +710,6 @@ def setdefault(self, key, value):
             self[key] = value
         return self[key]
 
-try:
-    _putenv = putenv
-except NameError:
-    _putenv = lambda key, value: None
-else:
-    if "putenv" not in __all__:
-        __all__.append("putenv")
-
-try:
-    _unsetenv = unsetenv
-except NameError:
-    _unsetenv = lambda key: _putenv(key, "")
-else:
-    if "unsetenv" not in __all__:
-        __all__.append("unsetenv")
-
 def _createenviron():
     if name == 'nt':
         # Where Env Var Names Must Be UPPERCASE
@@ -755,8 +737,7 @@ def decode(value):
         data = environ
     return _Environ(data,
         encodekey, decode,
-        encode, decode,
-        _putenv, _unsetenv)
+        encode, decode)
 
 # unicode environ
 environ = _createenviron()
@@ -781,8 +762,7 @@ def _check_bytes(value):
     # bytes environ
     environb = _Environ(environ._data,
         _check_bytes, bytes,
-        _check_bytes, bytes,
-        _putenv, _unsetenv)
+        _check_bytes, bytes)
     del _check_bytes
 
     def getenvb(key, default=None):

Lib/test/test_os.py

@@ -953,8 +953,6 @@ def test_environb(self):
         value_str = value.decode(sys.getfilesystemencoding(), 'surrogateescape')
         self.assertEqual(os.environ['bytes'], value_str)
 
-    @unittest.skipUnless(hasattr(os, 'putenv'), "Test needs os.putenv()")
-    @unittest.skipUnless(hasattr(os, 'unsetenv'), "Test needs os.unsetenv()")
     def test_putenv_unsetenv(self):
         name = "PYTHONTESTVAR"
         value = "testvalue"
@@ -975,8 +973,6 @@ def test_putenv_unsetenv(self):
 
     # On OS X < 10.6, unsetenv() doesn't return a value (bpo-13415).
     @support.requires_mac_ver(10, 6)
-    @unittest.skipUnless(hasattr(os, 'putenv'), "Test needs os.putenv()")
-    @unittest.skipUnless(hasattr(os, 'unsetenv'), "Test needs os.unsetenv()")
     def test_putenv_unsetenv_error(self):
         # Empty variable name is invalid.
         # "=" and null character are not allowed in a variable name.

Lib/test/test_posix.py

@@ -969,7 +969,6 @@ def test_environ(self):
             self.assertEqual(type(k), item_type)
             self.assertEqual(type(v), item_type)
 
-    @unittest.skipUnless(hasattr(os, "putenv"), "requires os.putenv()")
     def test_putenv(self):
         with self.assertRaises(ValueError):
             os.putenv('FRUIT\0VEGETABLE', 'cabbage')

Misc/NEWS.d/next/Build/2020-01-23-03-05-13.bpo-39395.RoArIZ.rst

@@ -0,0 +1,2 @@
+On non-Windows platforms, the :c:func:`setenv` and :c:func:`unsetenv` functions
+are now required to build Python.

Misc/NEWS.d/next/Library/2020-01-23-03-05-41.bpo-39395.4dda42.rst

@@ -0,0 +1,2 @@
+The :func:`os.putenv` and :func:`os.unsetenv` functions are now always
+available.