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Fix percent-format precision and integer conversion #8876

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Merged
youknowone merged 2 commits into from
Sep 28, 2026
Merged

Fix percent-format precision and integer conversion #8876

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640e19f
Fix percent-format precision and integer conversion
1ndahous3 Sep 27, 2026
008ee45
Honor float subclass integer conversions in percent formatting
1ndahous3 Sep 27, 2026
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164 changes: 62 additions & 102 deletions crates/vm/src/cformat.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,35 @@ use crate::{
stdlib::builtins,
};

fn format_decimal_object(
vm: &VirtualMachine,
spec: &CFormatSpec,
obj: &PyObject,
) -> PyResult<String> {
let type_error = || {
vm.new_type_error(format!(
"%{} format: a real number is required, not {}",
spec.format_type.to_char(),
obj.class().slot_name()
))
};
// Decimal conversions prefer __int__; __index__ is only a fallback when absent.
let i = obj
.number()
.int(vm)
.or_else(|| obj.try_index_opt(vm))
.ok_or_else(type_error)?
.map_err(|error| {
if error.fast_isinstance(vm.ctx.exceptions.type_error) {
type_error()
} else {
error
}
})?;
check_int_to_str_digits(i.as_bigint(), vm)?;
Ok(spec.format_number(i.as_bigint()))
}

fn spec_format_bytes(
vm: &VirtualMachine,
spec: &CFormatSpec,
Expand Down Expand Up @@ -69,40 +98,16 @@ fn spec_format_bytes(
}
CFormatType::Number(number_type) => match number_type {
CNumberType::DecimalD | CNumberType::DecimalI | CNumberType::DecimalU => {
match_class!(match &obj {
ref i @ PyInt => {
check_int_to_str_digits(i.as_bigint(), vm)?;
Ok(spec.format_number(i.as_bigint()).into_bytes())
}
ref f @ PyFloat => {
let bigint = try_f64_to_bigint(f.to_f64(), vm)?;
check_int_to_str_digits(&bigint, vm)?;
Ok(spec.format_number(&bigint).into_bytes())
}
obj => {
// CPython parity: `%d` / `%i` / `%u` accept any object
// with `__index__` (preferred) or `__int__`.
if let Some(int_result) = obj.try_index_opt(vm) {
let i = int_result?;
check_int_to_str_digits(i.as_bigint(), vm)?;
return Ok(spec.format_number(i.as_bigint()).into_bytes());
}

if let Some(method) = vm.get_method(obj.clone(), identifier!(vm, __int__)) {
let result = method?.call((), vm)?;
if let Some(i) = result.downcast_ref::<PyInt>() {
check_int_to_str_digits(i.as_bigint(), vm)?;
return Ok(spec.format_number(i.as_bigint()).into_bytes());
}
}

Err(vm.new_type_error(format!(
"%{} format: a real number is required, not {}",
spec.format_type.to_char(),
obj.class().slot_name()
)))
}
})
if let Some(i) = obj.downcast_ref::<PyInt>() {
check_int_to_str_digits(i.as_bigint(), vm)?;
Ok(spec.format_number(i.as_bigint()).into_bytes())
} else if let Some(f) = obj.downcast_ref_if_exact::<PyFloat>(vm) {
let bigint = try_f64_to_bigint(f.to_f64(), vm)?;
check_int_to_str_digits(&bigint, vm)?;
Ok(spec.format_number(&bigint).into_bytes())
} else {
format_decimal_object(vm, spec, &obj).map(String::into_bytes)
}
}
_ => {
// CPython parity: `%x` / `%o` / `%X` accept any object with
Expand Down Expand Up @@ -198,38 +203,16 @@ fn spec_format_string(
}
CFormatType::Number(number_type) => match number_type {
CNumberType::DecimalD | CNumberType::DecimalI | CNumberType::DecimalU => {
match_class!(match &obj {
ref i @ PyInt => {
check_int_to_str_digits(i.as_bigint(), vm)?;
Ok(spec.format_number(i.as_bigint()).into())
}
ref f @ PyFloat => {
let bigint = try_f64_to_bigint(f.to_f64(), vm)?;
check_int_to_str_digits(&bigint, vm)?;
Ok(spec.format_number(&bigint).into())
}
obj => {
// CPython parity: `%d` / `%i` / `%u` accept any object
// with `__index__` (preferred) or `__int__`.
if let Some(int_result) = obj.try_index_opt(vm) {
let i = int_result?;
check_int_to_str_digits(i.as_bigint(), vm)?;
return Ok(spec.format_number(i.as_bigint()).into());
}
if let Some(method) = vm.get_method(obj.clone(), identifier!(vm, __int__)) {
let result = method?.call((), vm)?;
if let Some(i) = result.downcast_ref::<PyInt>() {
check_int_to_str_digits(i.as_bigint(), vm)?;
return Ok(spec.format_number(i.as_bigint()).into());
}
}
Err(vm.new_type_error(format!(
"%{} format: a real number is required, not {}",
spec.format_type.to_char(),
obj.class().slot_name()
)))
}
})
if let Some(i) = obj.downcast_ref::<PyInt>() {
check_int_to_str_digits(i.as_bigint(), vm)?;
Ok(spec.format_number(i.as_bigint()).into())
} else if let Some(f) = obj.downcast_ref_if_exact::<PyFloat>(vm) {
let bigint = try_f64_to_bigint(f.to_f64(), vm)?;
check_int_to_str_digits(&bigint, vm)?;
Ok(spec.format_number(&bigint).into())
} else {
format_decimal_object(vm, spec, &obj).map(Into::into)
}
}
_ => {
// CPython parity: `%x` / `%o` / `%X` accept any object with
Expand Down Expand Up @@ -285,37 +268,11 @@ fn spec_format_string(
}
}

fn try_update_quantity_from_element(
vm: &VirtualMachine,
element: Option<&PyObject>,
) -> PyResult<CFormatQuantity> {
match element {
Some(width_obj) => {
if let Some(i) = width_obj.downcast_ref::<PyInt>() {
let i = i.try_to_primitive::<i32>(vm)?.unsigned_abs();
Ok(CFormatQuantity::Amount(i as usize))
} else {
Err(vm.new_type_error("* wants int"))
}
}
None => Err(vm.new_type_error("not enough arguments for format string")),
}
}

fn try_conversion_flag_from_tuple(
vm: &VirtualMachine,
element: Option<&PyObject>,
) -> PyResult<CConversionFlags> {
fn get_star_arg(vm: &VirtualMachine, element: Option<&PyObject>) -> PyResult<i32> {
match element {
Some(width_obj) => {
if let Some(i) = width_obj.downcast_ref::<PyInt>() {
let i = i.try_to_primitive::<i32>(vm)?;
let flags = if i < 0 {
CConversionFlags::LEFT_ADJUST
} else {
CConversionFlags::from_bits(0).unwrap()
};
Ok(flags)
Some(obj) => {
if let Some(i) = obj.downcast_ref::<PyInt>() {
i.try_to_primitive::<i32>(vm)
} else {
Err(vm.new_type_error("* wants int"))
}
Expand All @@ -334,10 +291,11 @@ fn try_update_quantity_from_tuple<'a, I: Iterator<Item = &'a PyObject>>(
return Ok(());
};

let element = elements.next();
f.insert(try_conversion_flag_from_tuple(vm, element)?);
let quantity = try_update_quantity_from_element(vm, element)?;
*q = Some(quantity);
let width = get_star_arg(vm, elements.next())?;
if width < 0 {
f.insert(CConversionFlags::LEFT_ADJUST);
}
*q = Some(CFormatQuantity::Amount(width.unsigned_abs() as usize));
Ok(())
}

Expand All @@ -350,8 +308,10 @@ fn try_update_precision_from_tuple<'a, I: Iterator<Item = &'a PyObject>>(
return Ok(());
};

let quantity = try_update_quantity_from_element(vm, elements.next())?;
*p = Some(CFormatPrecision::Quantity(quantity));
let precision = get_star_arg(vm, elements.next())?.max(0) as usize;
*p = Some(CFormatPrecision::Quantity(CFormatQuantity::Amount(
precision,
)));
Ok(())
}

Expand Down
8 changes: 8 additions & 0 deletions extra_tests/snippets/builtin_bytes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -644,6 +644,14 @@
# mod
assert b"rust%bpython%b" % (b" ", b"!") == b"rust python!"
assert b"x=%i y=%f" % (1, 2.5) == b"x=1 y=2.500000"
for precision in (-1, -3, -(2**31)):
assert b"%.*b" % (precision, b"hello") == b""
assert b"%.*s" % (-3, bytearray(b"hello")) == b""
assert b"%.*a" % (-3, "hello") == b""
assert b"%*.*d" % (-6, -3, 12) == b"12 "
assert b"%.*f" % (-3, 1.25) == b"1"
assert_raises(OverflowError, b"%.*b".__mod__, (-(2**31) - 1, b"abc"))
assert_raises(TypeError, b"%.*b".__mod__, (1.0, b"abc"))


# __bytes__
Expand Down
60 changes: 60 additions & 0 deletions extra_tests/snippets/builtin_str.py
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Original file line number Diff line number Diff line change
Expand Up @@ -338,6 +338,66 @@ def __repr__(self):
# Printf-style String formatting
assert "%d %d" % (1, 2) == "1 2"
assert "%*c " % (3, "❤") == " ❤ "
for precision in (-1, -3, -(2**31)):
assert "%.*s" % (precision, "🐍hello") == ""
assert "%*.*d" % (-6, -3, 12) == "12 "
assert "%.*f" % (-3, 1.25) == "1"
assert "%.*g" % (-3, 12.5) == "1e+01"
assert_raises(OverflowError, "%.*s".__mod__, (-(2**31) - 1, "abc"))
assert_raises(TypeError, "%.*s".__mod__, (1.0, "abc"))


class PercentIndex:
def __index__(self):
return 7


class PercentInt(PercentIndex):
def __init__(self, value):
self.value = value

def __int__(self):
if isinstance(self.value, Exception):
raise self.value
return self.value


class PercentFloat(float):
__int__ = PercentInt.__int__
__index__ = PercentIndex.__index__


class PercentFloatIndex(float):
__index__ = PercentIndex.__index__


class PercentIntSubclass(int):
def __int__(self):
raise AssertionError("int subclasses must use their stored value")


for template in ("%d", "%i", "%u", b"%d", b"%i", b"%u"):
assert template % PercentInt(3) == template % 3
assert template % PercentIndex() == template % 7
for value in (None, TypeError("conversion failed")):
with assert_raises(TypeError) as cm:
template % PercentInt(value)
assert str(cm.exception).endswith("a real number is required, not PercentInt")
assert_raises(
RuntimeError, template.__mod__, PercentInt(RuntimeError("conversion failed"))
)
number = PercentFloat(1.25)
number.value = 3
assert template % number == template % 3
number.value = None
assert_raises(TypeError, template.__mod__, number)
number.value = RuntimeError("conversion failed")
assert_raises(RuntimeError, template.__mod__, number)
assert template % PercentFloatIndex(1.25) == template % 1
assert template % PercentIntSubclass(1) == template % 1
assert "%x" % PercentInt(3) == "7"
assert b"%o" % PercentInt(3) == b"7"

assert (
"%(first)s %(second)s" % {"second": "World!", "first": "Hello,"} == "Hello, World!"
)
Expand Down
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