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gh-143715: Deprecate incomplete initialization of struct.Struct() #145580

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Merged
serhiy-storchaka merged 38 commits into from
Mar 12, 2026
Merged

gh-143715: Deprecate incomplete initialization of struct.Struct() #145580

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fff147f
gh-78724: deprecate incomplete initialization of struct.Struct()
skirpichev Jan 10, 2026
d2a0345
Merge branch 'master' into deprecate-struct-init-2/78724
skirpichev Jan 12, 2026
589fbc7
address review: test_Struct_reinitialization()
skirpichev Jan 12, 2026
5e91e87
catch new warning in test_operations_on_half_initialized_Struct()
skirpichev Jan 12, 2026
babb274
add init_called flag
skirpichev Jan 12, 2026
0e4e84b
Merge branch 'master' into deprecate-struct-init-2/78724
skirpichev Jan 13, 2026
3f36635
a hack to support new idiom for subclassing
skirpichev Jan 13, 2026
e576475
Merge branch 'master' into deprecate-struct-init-2/78724
skirpichev Jan 17, 2026
628aadd
+ filter out Struct signature test
skirpichev Jan 17, 2026
979cc18
Update Modules/_struct.c
skirpichev Jan 19, 2026
f7492ec
Merge branch 'master' into deprecate-struct-init-2/78724
skirpichev Jan 19, 2026
db8f5f2
address review: reformat s_new()
skirpichev Jan 19, 2026
dc8cbef
address review: actual___init___impl -> s_init
skirpichev Jan 19, 2026
6206ae1
Merge branch 'master' into deprecate-struct-init-2/78724
skirpichev Feb 22, 2026
12143d1
Update Doc/deprecations/pending-removal-in-3.20.rst
skirpichev Feb 25, 2026
d4ca6b8
Merge branch 'master' into deprecate-struct-init-2/78724
skirpichev Feb 25, 2026
6b9b4fb
+ rename news
skirpichev Feb 25, 2026
79961a2
Apply suggestions from code review
skirpichev Feb 25, 2026
58550c0
address review: add test
skirpichev Feb 25, 2026
c815882
address review: fix for format
skirpichev Feb 25, 2026
f1388ee
address review: reformat if blocks
skirpichev Feb 25, 2026
685a6c4
address review: s_new
skirpichev Feb 25, 2026
76f8723
Merge branch 'master' into deprecate-struct-init-2/78724
skirpichev Feb 26, 2026
538d301
address review: add fake signature for Struct
skirpichev Feb 26, 2026
09d6ebd
+test new idiom
skirpichev Feb 27, 2026
7f0a133
Some cleanup; also add reference to issue and reverted PR
skirpichev Feb 28, 2026
26cde89
Merge branch 'master' into deprecate-struct-init-2/78724
skirpichev Feb 28, 2026
7697820
issue DeprecationWarning for implicit tp_new calls in subclasses
skirpichev Feb 28, 2026
05eb292
Fix more corner cases.
serhiy-storchaka Mar 6, 2026
d9c0488
Update credicts.
serhiy-storchaka Mar 7, 2026
3de045b
Fix format for the __sizeof__ test.
serhiy-storchaka Mar 7, 2026
ebcf358
Fix test_Struct_reinitialization on big-endian and add tests for inva…
serhiy-storchaka Mar 9, 2026
e003dab
Add assertions for format.
serhiy-storchaka Mar 9, 2026
d453990
Factorize some tests.
serhiy-storchaka Mar 10, 2026
66dbc04
Merge branch 'main' into deprecate-struct-init
serhiy-storchaka Mar 10, 2026
6d60b16
Update Doc/deprecations/pending-removal-in-3.20.rst
serhiy-storchaka Mar 11, 2026
d7da0f8
Merge branch 'main' into deprecate-struct-init
serhiy-storchaka Mar 11, 2026
ca960a8
Emit FutureWarning instead of DeprecationWarning for re-initialization.
serhiy-storchaka Mar 11, 2026
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Add assertions for format.
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@serhiy-storchaka
serhiy-storchaka committed Mar 9, 2026
commit e003dab66580fda281f7a1b1963161af2252dc81
12 changes: 12 additions & 0 deletions Lib/test/test_struct.py
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Original file line number Diff line number Diff line change
Expand Up @@ -880,20 +880,28 @@ def __new__(cls, *args, **kwargs):
return super().__new__(cls, '>h')

my_struct = MyStruct('>h')
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@vstinner vstinner Mar 10, 2026

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You can factorize some tests using ony 1 positional argument:

        for format in ('>h', '<h', 42, '$', '\u20ac'):
            with self.subTest(format=format):
                my_struct = MyStruct(format)
                self.assertEqual(my_struct.format, '>h')
                self.assertEqual(my_struct.pack(12345), b'\x30\x39')

self.assertEqual(my_struct.format, '>h')
self.assertEqual(my_struct.pack(12345), b'\x30\x39')
my_struct = MyStruct('<h')
self.assertEqual(my_struct.format, '>h')
self.assertEqual(my_struct.pack(12345), b'\x30\x39')
my_struct = MyStruct(format='<h')
self.assertEqual(my_struct.format, '>h')
self.assertEqual(my_struct.pack(12345), b'\x30\x39')
my_struct = MyStruct()
self.assertEqual(my_struct.format, '>h')
self.assertEqual(my_struct.pack(12345), b'\x30\x39')
my_struct = MyStruct(42)
self.assertEqual(my_struct.format, '>h')
self.assertEqual(my_struct.pack(12345), b'\x30\x39')
my_struct = MyStruct('$')
self.assertEqual(my_struct.format, '>h')
self.assertEqual(my_struct.pack(12345), b'\x30\x39')
my_struct = MyStruct('\u20ac')
self.assertEqual(my_struct.format, '>h')
self.assertEqual(my_struct.pack(12345), b'\x30\x39')
my_struct = MyStruct('<h', 42)
self.assertEqual(my_struct.format, '>h')
self.assertEqual(my_struct.pack(12345), b'\x30\x39')

def test_custom_struct_new_and_init(self):
Expand All @@ -906,6 +914,7 @@ def __init__(self, newargs, initargs):
super().__init__(*initargs)

my_struct = MyStruct(('>h',), ('>h',))
Comment on lines +904 to +912
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@skirpichev skirpichev Mar 7, 2026

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Again, why no warnings here?

BTW, I doubt this usage pattern come from reality ;-)

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@serhiy-storchaka serhiy-storchaka Mar 7, 2026

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Because __new__() and __init__() are called with the same argument, as expected. You are supposed to do this if you write a code that works in all versions.

As for other cases, having both custom __new__() and __init__() which call corresponding parent's methods with different arguments is unusual, but this need to be tested. I found bugs in my code when added these tests.

self.assertEqual(my_struct.format, '>h')
self.assertEqual(my_struct.pack(12345), b'\x30\x39')
with self.assertRaises(TypeError):
MyStruct((), ())
Expand All @@ -930,15 +939,18 @@ def __init__(self, newargs, initargs):
MyStruct(('>h',), ('\u20ac',))
with self.assertWarns(FutureWarning):
my_struct = MyStruct(('>h',), ('<h',))
self.assertEqual(my_struct.format, '<h')
self.assertEqual(my_struct.pack(12345), b'\x39\x30')

def test_no_custom_struct_new_or_init(self):
class MyStruct(struct.Struct):
pass

my_struct = MyStruct('>h')
self.assertEqual(my_struct.format, '>h')
self.assertEqual(my_struct.pack(12345), b'\x30\x39')
my_struct = MyStruct(format='>h')
self.assertEqual(my_struct.format, '>h')
self.assertEqual(my_struct.pack(12345), b'\x30\x39')
with self.assertRaises(TypeError):
MyStruct()
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