`test_functools` unexpected failures when C `_functoolsmodule` is missing

[sobolevn]

BPO	46647
Nosy	@rhettinger, @tiran, @shihai1991, @sobolevn
PRs	bpo-46647: make sure test_functools works with and without _functoolsmodule #31141

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2022-02-08.04:43:59.900>
created_at = <Date 2022-02-05.10:46:54.761>
labels = ['type-bug', 'tests', '3.10', '3.11']
title = '`test_functools` unexpected failures when C `_functoolsmodule` is missing'
updated_at = <Date 2022-02-08.04:43:59.899>
user = 'https://github.com/sobolevn'

bugs.python.org fields:

activity = <Date 2022-02-08.04:43:59.899>
actor = 'sobolevn'
assignee = 'none'
closed = True
closed_date = <Date 2022-02-08.04:43:59.900>
closer = 'sobolevn'
components = ['Tests']
creation = <Date 2022-02-05.10:46:54.761>
creator = 'sobolevn'
dependencies = []
files = []
hgrepos = []
issue_num = 46647
keywords = ['patch']
message_count = 5.0
messages = ['412565', '412572', '412573', '412767', '412809']
nosy_count = 4.0
nosy_names = ['rhettinger', 'christian.heimes', 'shihai1991', 'sobolevn']
pr_nums = ['31141']
priority = 'normal'
resolution = 'wont fix'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue46647'
versions = ['Python 3.10', 'Python 3.11']

Linked PRs

• gh-90805: make sure test_functools works with and without _functoolsmodule #108644
• [3.11] gh-90805: Make sure test_functools works with and without _functoolsmodule (GH-108644) #109274
• [3.12] gh-90805: Make sure test_functools works with and without _functoolsmodule (GH-108644) #109275

[sobolevn]

Reproduction steps:

1. Add to Setup.local:

*disabled*
_functoolsmodule

2. .configure && make -j. Then, ensure that this module is not available:

» ./python.exe -c 'import _functools'                                         
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ModuleNotFoundError: No module named '_functools'

3. Run test_functools:

======================================================================
ERROR: test_bad_cmp (test.test_functools.TestCmpToKeyC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 905, in test_bad_cmp
    key = self.cmp_to_key(cmp1)
          ^^^^^^^^^^^^^^^^^^^^^
TypeError: cmp_to_key() takes 1 positional argument but 2 were given

======================================================================
ERROR: test_cmp_to_key (test.test_functools.TestCmpToKeyC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 869, in test_cmp_to_key
    key = self.cmp_to_key(cmp1)
          ^^^^^^^^^^^^^^^^^^^^^
TypeError: cmp_to_key() takes 1 positional argument but 2 were given

======================================================================
ERROR: test_cmp_to_key_arguments (test.test_functools.TestCmpToKeyC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 885, in test_cmp_to_key_arguments
    key = self.cmp_to_key(mycmp=cmp1)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: cmp_to_key() got multiple values for argument 'mycmp'

======================================================================
ERROR: test_hash (test.test_functools.TestCmpToKeyC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 941, in test_hash
    key = self.cmp_to_key(mycmp)
          ^^^^^^^^^^^^^^^^^^^^^^
TypeError: cmp_to_key() takes 1 positional argument but 2 were given

======================================================================
ERROR: test_obj_field (test.test_functools.TestCmpToKeyC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 920, in test_obj_field
    key = self.cmp_to_key(mycmp=cmp1)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: cmp_to_key() got multiple values for argument 'mycmp'

======================================================================
ERROR: test_sort_int (test.test_functools.TestCmpToKeyC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 926, in test_sort_int
    self.assertEqual(sorted(range(5), key=self.cmp_to_key(mycmp)),
                                          ^^^^^^^^^^^^^^^^^^^^^^
TypeError: cmp_to_key() takes 1 positional argument but 2 were given

======================================================================
ERROR: test_sort_int_str (test.test_functools.TestCmpToKeyC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 934, in test_sort_int_str
    values = sorted(values, key=self.cmp_to_key(mycmp))
                                ^^^^^^^^^^^^^^^^^^^^^^
TypeError: cmp_to_key() takes 1 positional argument but 2 were given

======================================================================
ERROR: test_pickle (test.test_functools.TestPartialC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 258, in test_pickle
    f_copy = pickle.loads(pickle.dumps(f, proto))
                          ^^^^^^^^^^^^^^^^^^^^^^
_pickle.PicklingError: Can't pickle <class 'functools.partial'>: it's not the same object as functools.partial

======================================================================
ERROR: test_recursive_pickle (test.test_functools.TestPartialC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 343, in test_recursive_pickle
    pickle.dumps(f, proto)
    ^^^^^^^^^^^^^^^^^^^^^^
_pickle.PicklingError: Can't pickle <class 'functools.partial'>: it's not the same object as functools.partial

======================================================================
ERROR: test_iterator_usage (test.test_functools.TestReduceC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 843, in test_iterator_usage
    self.assertEqual(self.reduce(add, SequenceClass(5)), 10)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/sobolev/Desktop/cpython/Lib/functools.py", line 249, in reduce
    it = iter(sequence)
         ^^^^^^^^^^^^^^
TypeError: 'builtin_function_or_method' object is not iterable

======================================================================
ERROR: test_reduce (test.test_functools.TestReduceC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 794, in test_reduce
    self.assertEqual(self.reduce(add, ['a', 'b', 'c'], ''), 'abc')
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: reduce() takes from 2 to 3 positional arguments but 4 were given

======================================================================
FAIL: test_disallow_instantiation (test.test_functools.TestCmpToKeyC)
----------------------------------------------------------------------
TypeError: type() takes 1 or 3 arguments

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 955, in test_disallow_instantiation
    support.check_disallow_instantiation(
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/sobolev/Desktop/cpython/Lib/test/support/__init__.py", line 2121, in check_disallow_instantiation
    testcase.assertRaisesRegex(TypeError, msg, tp, *args, **kwds)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: "cannot create 'type' instances" does not match "type() takes 1 or 3 arguments"

======================================================================
FAIL: test_attributes_unwritable (test.test_functools.TestPartialC)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 402, in test_attributes_unwritable
    self.assertRaises(AttributeError, setattr, p, 'func', map)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: AttributeError not raised by setattr

======================================================================
FAIL: test_attributes_unwritable (test.test_functools.TestPartialCSubclass)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_functools.py", line 402, in test_attributes_unwritable
    self.assertRaises(AttributeError, setattr, p, 'func', map)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: AttributeError not raised by setattr

----------------------------------------------------------------------
Ran 249 tests in 0.690s

FAILED (failures=3, errors=11)
test test_functools failed
test_functools failed (11 errors, 3 failures)

== Tests result: FAILURE ==

1 test failed:
    test_functools

Total duration: 1.3 sec
Tests result: FAILURE

List of individual problems:

1. This function is defined assuming that c_functools always has .lru_cache:

   cpython/Lib/test/test_functools.py

   Lines 1860 to 1862 in fea7290

   	@c_functools.lru_cache()
   	def c_cached_func(x, y):
   	return 3 * x + y

2. TestLRUC is never skipped:

   cpython/Lib/test/test_functools.py

   Lines 1879 to 1881 in fea7290

   	class TestLRUC(TestLRU, unittest.TestCase):
   	module = c_functools
   	cached_func = c_cached_func,

   I think it should be, because there's no need to test _lru_cache_wrapper twice for just python implementation (default if _functools is missing)
3. All similar modules tend to use fresh= in import_fresh_module, for example:

   cpython/Lib/test/test_typing.py

   Lines 43 to 44 in fea7290

   	py_typing = import_helper.import_fresh_module('typing', blocked=['_typing'])
   	c_typing = import_helper.import_fresh_module('typing', fresh=['_typing'])

   But, test_functools does not do this:

   cpython/Lib/test/test_functools.py

   Line 30 in fea7290

   c_functools = import_helper.import_fresh_module('functools')

   So, even if _functools is missing, c_functools will not be None, it will still be functools.py module! And this causes multiple unexpected test failures above

Related:

• bpo-40137: Convert _functools module to use PyType_FromModuleAndSpec. #23405
• bpo-42410: Resolve pickleError in case typeobject is heaptypeobject. #23407

I will send a patch for this in a moment.

[tiran]

_functoolsmodule is a core bootstrap module and defined in Modules/Setup.bootstrap. It has no external dependencies. There is no reason and no point to disable the module.

We can safely assume that all modules defined in Modules/Setup.bootstrap are always available. (Maybe except for pwd, but that is a different story.)

I propose to close the bug and PR as wontfix.

[sobolevn]

Cristian, in this case - is there a reason to keep skipUnless(c_functools) around?

If we are sure that it is always available - then it should be always tested.

We either should have:

1. Cleanly defined skips that work (this PR)
2. Unconditional coverage

Or do you think that some middle-ground is possible?

[shihai1991]

_functoolsmodule is a core bootstrap module and defined in Modules/Setup.bootstrap. It has no external dependencies. There is no reason and no point to disable the module.

+1.

Cristian, in this case - is there a reason to keep skipUnless(c_functools) around?
If we are sure that it is always available - then it should be always tested.

Hm. Personally, I suggest to keep the skipUnless to aovid the code churn.
Or maybe you have other cases to show the functools module will missing unexpectly?

[sobolevn]

Or maybe you have other cases to show the functools module will missing unexpectly?

No, I can't think of any :)

Your argument about code churn also makes sense.
But, if we ever are going to refactor this test module, this is something to remember of.

Thanks everyone!