[2.7] bpo-31692: Add PYTHONSHOWALLOCCOUNT env var (GH-3927)

bpo-31692, bpo-19527:

* Add a new PYTHONSHOWALLOCCOUNT environment variable, similar to
  the Python 3 "-X showalloccount" option
* When Python is compiled with COUNT_ALLOCS, the new
  PYTHONSHOWALLOCCOUNT environment variable now has to be set to dump
  allocation counts into stderr on shutdown. Moreover, allocations
  statistics are now dumped into stderr rather than stdout.
* Add @test.support.requires_type_collecting decorator: skip test if
  COUNT_ALLOCS is defined
* Fix tests for COUNT_ALLOCS: decorate some methods with
  @requires_type_collecting
* test_sys.test_objecttypes(): update object type when COUNT_ALLOCS
  is defined

Doc/c-api/typeobj.rst

@@ -1101,7 +1101,7 @@ The next fields, up to and including :c:member:`~PyTypeObject.tp_weaklist`, only
 The remaining fields are only defined if the feature test macro
 :const:`COUNT_ALLOCS` is defined, and are for internal use only. They are
 documented here for completeness.  None of these fields are inherited by
-subtypes.
+subtypes. See the :envvar:`PYTHONSHOWALLOCCOUNT` environment variable.
 
 
 .. c:member:: Py_ssize_t PyTypeObject.tp_allocs

Doc/using/cmdline.rst

@@ -664,6 +664,13 @@ if Python was configured with the ``--with-pydebug`` build option.
    If set, Python will print memory allocation statistics every time a new
    object arena is created, and on shutdown.
 
+.. envvar:: PYTHONSHOWALLOCCOUNT
+
+   If set and Python was compiled with ``COUNT_ALLOCS`` defined, Python will
+   dump allocations counts into stderr on shutdown.
+
+   .. versionadded:: 2.7.15
+
 .. envvar:: PYTHONSHOWREFCOUNT
 
    If set, Python will print the total reference count when the program

Lib/test/support/__init__.py

@@ -1795,6 +1795,9 @@ def py3k_bytes(b):
         except TypeError:
             return bytes(b)
 
+requires_type_collecting = unittest.skipIf(hasattr(sys, 'getcounts'),
+                        'types are immortal if COUNT_ALLOCS is defined')
+
 def args_from_interpreter_flags():
     """Return a list of command-line arguments reproducing the current
     settings in sys.flags."""

Lib/test/test_abc.py

@@ -208,6 +208,7 @@ class TestABC(unittest.TestCase):
         C()
         self.assertEqual(B.counter, 1)
 
+    @test_support.requires_type_collecting
     def test_cache_leak(self):
         # See issue #2521.
         class A(object):

Lib/test/test_gc.py

@@ -1,5 +1,6 @@
 import unittest
-from test.test_support import verbose, run_unittest, start_threads
+from test.support import (verbose, run_unittest, start_threads,
+                          requires_type_collecting)
 import sys
 import time
 import gc
@@ -90,6 +91,7 @@ class GCTests(unittest.TestCase):
         del a
         self.assertNotEqual(gc.collect(), 0)
 
+    @requires_type_collecting
     def test_newinstance(self):
         class A(object):
             pass

Lib/test/test_regrtest.py

@@ -493,6 +493,7 @@ class ArgsTestCase(BaseTestCase):
             self.assertIn(line2, reflog)
 
     @unittest.skipUnless(Py_DEBUG, 'need a debug build')
+    @support.requires_type_collecting
     def test_huntrleaks(self):
         # test --huntrleaks
         code = textwrap.dedent("""

Lib/test/test_sys.py

@@ -748,7 +748,10 @@ class SizeofTest(unittest.TestCase):
         # tupleiterator
         check(iter(()), size('lP'))
         # type
-        s = vsize('P2P15Pl4PP9PP11PI'   # PyTypeObject
+        fmt = 'P2P15Pl4PP9PP11PI'
+        if hasattr(sys, 'getcounts'):
+            fmt += '3P2P'
+        s = vsize(fmt +                 # PyTypeObject
                   '39P'                 # PyNumberMethods
                   '3P'                  # PyMappingMethods
                   '10P'                 # PySequenceMethods

Lib/test/test_weakref.py

@@ -601,6 +601,7 @@ class ReferencesTestCase(TestBase):
         del c1, c2, C, D
         gc.collect()
 
+    @test_support.requires_type_collecting
     def test_callback_in_cycle_resurrection(self):
         import gc
 

Misc/NEWS.d/next/Core and Builtins/2017-10-09-11-03-13.bpo-31692.5-bpdk.rst

@@ -0,0 +1,4 @@
+Add a new PYTHONSHOWALLOCCOUNT environment variable. When Python is compiled
+with COUNT_ALLOCS, PYTHONSHOWALLOCCOUNT now has to be set to dump allocation
+counts into stderr on shutdown. Moreover, allocations statistics are now dumped
+into stderr rather than stdout.

Python/pythonrun.c

@@ -488,7 +488,9 @@ Py_Finalize(void)
 
     /* Debugging stuff */
 #ifdef COUNT_ALLOCS
-    dump_counts(stdout);
+    if (Py_GETENV("PYTHONSHOWALLOCCOUNT")) {
+        dump_counts(stderr);
+    }
 #endif
 
     _PyDebug_PrintTotalRefs();