gh-143715: Deprecate incomplete initialization of struct.Struct()#145580
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serhiy-storchaka wants to merge 29 commits intopython:mainfrom
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gh-143715: Deprecate incomplete initialization of struct.Struct()#145580serhiy-storchaka wants to merge 29 commits intopython:mainfrom
serhiy-storchaka wants to merge 29 commits intopython:mainfrom
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* ``Struct.__new__()`` will require a mandatory argument (format) * Calls of ``__init__()`` method on initialized Struct are deprecated
This make format argument in the __init__() - optional. If it's missing, the object must be already initialized in __new__().
Co-authored-by: Victor Stinner <vstinner@python.org>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
This catch current pattern for Struct's subclassing like
class MyStruct(Struct):
def __init__(self):
super().__init__('>h')
skirpichev
reviewed
Mar 7, 2026
| :meth:`~object.__init__` method on initialized :class:`~struct.Struct` | ||
| objects is deprecated and will be removed in Python 3.20. | ||
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| (Contributed by Sergey B Kirpichev in :gh:`143715`.) |
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Suggested change
| (Contributed by Sergey B Kirpichev in :gh:`143715`.) | |
| (Contributed by Serhiy Storchaka in :gh:`143715`.) |
| :meth:`~object.__init__` method on initialized :class:`~struct.Struct` | ||
| objects is deprecated and will be removed in Python 3.20. | ||
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| (Contributed by Sergey B Kirpichev in :gh:`143715`.) |
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Suggested change
| (Contributed by Sergey B Kirpichev in :gh:`143715`.) | |
| (Contributed by Serhiy Storchaka in :gh:`143715`.) |
| def check_sizeof(self, format_str, number_of_codes): | ||
| # The size of 'PyStructObject' | ||
| totalsize = support.calcobjsize('2n3P') | ||
| totalsize = support.calcobjsize('2n3P1?') |
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Suggested change
| totalsize = support.calcobjsize('2n3P1?') | |
| totalsize = support.calcobjsize('2n3P?') |
| super().__init__('>h') | ||
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| my_struct = MyStruct('>h') | ||
| self.assertEqual(my_struct.pack(12345), b'\x30\x39') |
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I think this will be more clear, per Victor's suggestion:
Suggested change
| self.assertEqual(my_struct.pack(12345), b'\x30\x39') | |
| self.assertEqual(my_struct.format, '>h') |
(and in all cases below too)
| def __init__(self, *args, **kwargs): | ||
| super().__init__('>h') | ||
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| my_struct = MyStruct('>h') |
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Why this not raises a warning? I think we should warn in all cases, where Struct.__init__() was explicitly called. // #143659 (comment)
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| my_struct = MyStruct('>h') | ||
| self.assertEqual(my_struct.pack(12345), b'\x30\x39') | ||
| my_struct = MyStruct(format='>h') |
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Ah, I entirely forgot that format is a positional or keyword argument in the master. I'll fix my patch.
But again, this should emit a warning.
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| # New way, no warnings: | ||
| class MyStruct(struct.Struct): | ||
| def __new__(cls, newargs, initargs): | ||
| return super().__new__(cls, *newargs) | ||
| def __init__(self, newargs, initargs): | ||
| if initargs is not None: | ||
| super().__init__(*initargs) | ||
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| my_struct = MyStruct(('>h',), ('>h',)) |
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Again, why no warnings here?
BTW, I doubt this usage pattern come from reality ;-)
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Struct.__new__()will require a mandatory argument (format)__init__()method on initialized Struct are deprecatedThis is an evolution of #143659, but since virtually all code and test were rewritten I created a new PR.
📚 Documentation preview 📚: https://cpython-previews--145580.org.readthedocs.build/