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bpo-43988: Add test.support.check_disallow_instantiation #25757

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Merged
merged 1 commit into from
May 26, 2021
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bpo-43988: Add test.support.check_disallow_instantiation #25757

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11 changes: 11 additions & 0 deletions Lib/test/support/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@
"requires_IEEE_754", "requires_zlib",
"anticipate_failure", "load_package_tests", "detect_api_mismatch",
"check__all__", "skip_if_buggy_ucrt_strfptime",
"check_disallow_instantiation",
# sys
"is_jython", "is_android", "check_impl_detail", "unix_shell",
"setswitchinterval",
Expand Down Expand Up @@ -1982,3 +1983,13 @@ def skip_if_broken_multiprocessing_synchronize():
synchronize.Lock(ctx=None)
except OSError as exc:
raise unittest.SkipTest(f"broken multiprocessing SemLock: {exc!r}")


def check_disallow_instantiation(testcase, tp, *args, **kwds):
"""
Helper for testing types with the Py_TPFLAGS_DISALLOW_INSTANTIATION flag.

See bpo-43916.
"""
msg = f"cannot create '{tp.__module__}\.{tp.__name__}' instances"
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You should use f"xxx\.xxx" or fr"xxx.xxx". Or maybe use re.escape().

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@erlend-aasland erlend-aasland May 2, 2021 •
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Since these tests are decorated with cpython_only, it should be ok to match the exact string, as produced by Objects/typeobject.c? Just matching the type module/name could in theory generate wrong result; maybe not in practice though.

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What about setting the match pattern depending on what test.support.check_impl_detail() says?

testcase.assertRaisesRegex(TypeError, msg, tp, *args, **kwds)
6 changes: 3 additions & 3 deletions Lib/test/test_array.py
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Expand Up @@ -42,9 +42,9 @@ def test_bad_constructor(self):

@support.cpython_only
def test_disallow_instantiation(self):
# Ensure that the type disallows instantiation (bpo-43916)
tp = type(iter(array.array('I')))
self.assertRaises(TypeError, tp)
my_array = array.array("I")
tp = type(iter(my_array))
support.check_disallow_instantiation(self, tp, my_array)

@support.cpython_only
def test_immutable(self):
Expand Down