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Accept the format keyword in Struct initialization #9064

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Merged
youknowone merged 1 commit into from
Oct 10, 2026
Merged

Accept the format keyword in Struct initialization #9064

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11 changes: 9 additions & 2 deletions crates/stdlib/src/pystruct.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -289,10 +289,17 @@ pub(crate) mod _struct {
}
}

#[derive(FromArgs)]
struct StructArgs {
#[pyarg(any)]
format: IntoStructFormatBytes,
}

impl Initializer for PyStruct {
type Args = IntoStructFormatBytes;
type Args = StructArgs;

fn init(zelf: &Py<Self>, fmt: Self::Args, vm: &VirtualMachine) -> PyResult<()> {
fn init(zelf: &Py<Self>, args: Self::Args, vm: &VirtualMachine) -> PyResult<()> {
let fmt = args.format;
// The format is read before anything is replaced, so a format that
// cannot be read leaves the object as it was.
let spec = fmt.format_spec(vm)?;
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18 changes: 18 additions & 0 deletions extra_tests/snippets/stdlib_struct.py
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Expand Up @@ -184,3 +184,21 @@ def __index__(self):
buffer = bytearray(2)
struct.pack_into("<H", buffer, 0, ClearFormats())
assert buffer == b"\x2a\x00"


# Struct's format is positional-or-keyword, including inherited initialization.
class KeywordStruct(struct.Struct):
pass


for cls in (struct.Struct, KeywordStruct):
for fmt in (">h", b">h"):
s = cls(format=fmt)
assert s.format == ">h"
assert s.pack(7) == b"\x00\x07"
s.__init__(format=">hh")
assert s.unpack(b"\x00\x01\x00\x02") == (1, 2)
with assert_raises(struct.error):
s.__init__(format="$")
assert s.format == ">hh"
assert s.pack(1, 2) == b"\x00\x01\x00\x02"
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