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chore: Add DTypeClass to improve DType.__repr__ and simplify __slots__ #3213

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ca2824b
chore: DTypeClass metaclass
FBruzzesi Oct 14, 2025
cd26196
simplify
FBruzzesi Oct 14, 2025
e4bddda
Match Dan's impl in _plan/_meta.py
FBruzzesi Oct 14, 2025
cf42d29
merge main
FBruzzesi Oct 15, 2025
59dc3d9
Thanks Dan
FBruzzesi Oct 16, 2025
62c822f
Merge branch 'main' into chore/dtype-meta
FBruzzesi Oct 16, 2025
cdf38b3
test: Demonstrate repr quirk
dangotbanned Oct 16, 2025
fb1a4a0
test: xfail for now
dangotbanned Oct 17, 2025
1bb2dd4
refactor: Use `DTypeClass` instead of `type`
dangotbanned Oct 17, 2025
431dbf3
Merge remote-tracking branch 'upstream/main' into chore/dtype-meta
dangotbanned Oct 17, 2025
0144e6c
refactor: don't import twice 😄
dangotbanned Oct 17, 2025
85210de
Change from `*` to `-` for markdown list
FBruzzesi Oct 17, 2025
448f8d6
merge main, solve conflicts
FBruzzesi Oct 20, 2025
73d015b
Merge branch 'main' into chore/dtype-meta
FBruzzesi Oct 22, 2025
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121 changes: 45 additions & 76 deletions narwhals/dtypes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@
from collections.abc import Iterator, Sequence
from typing import Any

import _typeshed
from typing_extensions import Self, TypeIs

from narwhals.typing import IntoDType, TimeUnit
Expand All @@ -33,14 +34,12 @@ def _validate_dtype(dtype: DType | type[DType]) -> None:

def _is_into_dtype(obj: Any) -> TypeIs[IntoDType]:
return isinstance(obj, DType) or (
isinstance(obj, type)
and issubclass(obj, DType)
and not issubclass(obj, NestedType)
isinstance(obj, DTypeClass) and not issubclass(obj, NestedType)
)


def _is_nested_type(obj: Any) -> TypeIs[type[NestedType]]:
return isinstance(obj, type) and issubclass(obj, NestedType)
return isinstance(obj, DTypeClass) and issubclass(obj, NestedType)


def _validate_into_dtype(dtype: Any) -> None:
Expand All @@ -59,10 +58,40 @@ def _validate_into_dtype(dtype: Any) -> None:
raise TypeError(msg)


class DType:
__slots__ = ()
class DTypeClass(type):
"""Metaclass for DType classes.

def __repr__(self) -> str: # pragma: no cover
* Nicely print classes.
* Ensure [`__slots__`] are always defined to prevent `__dict__` creation (empty by default).

[`__slots__`]: https://docs.python.org/3/reference/datamodel.html#object.__slots__
"""

def __repr__(cls) -> str:
return cls.__name__

# https://github.com/python/typeshed/blob/776508741d76b58f9dcb2aaf42f7d4596a48d580/stdlib/abc.pyi#L13-L19
# https://github.com/python/typeshed/blob/776508741d76b58f9dcb2aaf42f7d4596a48d580/stdlib/_typeshed/__init__.pyi#L36-L40
# https://github.com/astral-sh/ruff/issues/8353#issuecomment-1786238311
# https://docs.python.org/3/reference/datamodel.html#creating-the-class-object
def __new__(
metacls: type[_typeshed.Self],
cls_name: str,
bases: tuple[type, ...],
namespace: dict[str, Any],
/,
**kwds: Any,
) -> _typeshed.Self:
namespace.setdefault("__slots__", ())
return super().__new__(metacls, cls_name, bases, namespace, **kwds) # type: ignore[no-any-return, misc]


class DType(metaclass=DTypeClass):
"""Base class for all Narwhals data types."""

__slots__ = () # NOTE: Keep this one defined manually for the type checker

def __repr__(self) -> str:
return self.__class__.__qualname__

@classmethod
Expand All @@ -72,13 +101,11 @@ def base_type(cls) -> type[Self]:
Examples:
>>> import narwhals as nw
>>> nw.Datetime("us").base_type()
<class 'narwhals.dtypes.Datetime'>

Datetime
>>> nw.String.base_type()
<class 'narwhals.dtypes.String'>

String
>>> nw.List(nw.Int64).base_type()
<class 'narwhals.dtypes.List'>
List
"""
return cls

Expand Down Expand Up @@ -143,8 +170,6 @@ def __eq__(self, other: DType | type[DType]) -> bool: # type: ignore[override]
>>> nw.Date() == nw.Datetime
False
"""
from narwhals._utils import isinstance_or_issubclass

return isinstance_or_issubclass(other, type(self))

def __hash__(self) -> int:
Expand All @@ -154,44 +179,30 @@ def __hash__(self) -> int:
class NumericType(DType):
"""Base class for numeric data types."""

__slots__ = ()


class IntegerType(NumericType):
"""Base class for integer data types."""

__slots__ = ()


class SignedIntegerType(IntegerType):
"""Base class for signed integer data types."""

__slots__ = ()


class UnsignedIntegerType(IntegerType):
"""Base class for unsigned integer data types."""

__slots__ = ()


class FloatType(NumericType):
"""Base class for float data types."""

__slots__ = ()


class TemporalType(DType):
"""Base class for temporal data types."""

__slots__ = ()


class NestedType(DType):
"""Base class for nested data types."""

__slots__ = ()


class Decimal(NumericType):
"""Decimal type.
Expand All @@ -204,8 +215,6 @@ class Decimal(NumericType):
Decimal
"""

__slots__ = ()


class Int128(SignedIntegerType):
"""128-bit signed integer type.
Expand All @@ -226,8 +235,6 @@ class Int128(SignedIntegerType):
Int128
"""

__slots__ = ()


class Int64(SignedIntegerType):
"""64-bit signed integer type.
Expand All @@ -241,8 +248,6 @@ class Int64(SignedIntegerType):
Int64
"""

__slots__ = ()


class Int32(SignedIntegerType):
"""32-bit signed integer type.
Expand All @@ -256,8 +261,6 @@ class Int32(SignedIntegerType):
Int32
"""

__slots__ = ()


class Int16(SignedIntegerType):
"""16-bit signed integer type.
Expand All @@ -271,8 +274,6 @@ class Int16(SignedIntegerType):
Int16
"""

__slots__ = ()


class Int8(SignedIntegerType):
"""8-bit signed integer type.
Expand All @@ -286,8 +287,6 @@ class Int8(SignedIntegerType):
Int8
"""

__slots__ = ()


class UInt128(UnsignedIntegerType):
"""128-bit unsigned integer type.
Expand All @@ -302,8 +301,6 @@ class UInt128(UnsignedIntegerType):
UInt128
"""

__slots__ = ()


class UInt64(UnsignedIntegerType):
"""64-bit unsigned integer type.
Expand All @@ -317,8 +314,6 @@ class UInt64(UnsignedIntegerType):
UInt64
"""

__slots__ = ()


class UInt32(UnsignedIntegerType):
"""32-bit unsigned integer type.
Expand All @@ -332,8 +327,6 @@ class UInt32(UnsignedIntegerType):
UInt32
"""

__slots__ = ()


class UInt16(UnsignedIntegerType):
"""16-bit unsigned integer type.
Expand All @@ -347,8 +340,6 @@ class UInt16(UnsignedIntegerType):
UInt16
"""

__slots__ = ()


class UInt8(UnsignedIntegerType):
"""8-bit unsigned integer type.
Expand All @@ -362,8 +353,6 @@ class UInt8(UnsignedIntegerType):
UInt8
"""

__slots__ = ()


class Float64(FloatType):
"""64-bit floating point type.
Expand All @@ -377,8 +366,6 @@ class Float64(FloatType):
Float64
"""

__slots__ = ()


class Float32(FloatType):
"""32-bit floating point type.
Expand All @@ -392,8 +379,6 @@ class Float32(FloatType):
Float32
"""

__slots__ = ()


class String(DType):
"""UTF-8 encoded string type.
Expand All @@ -406,8 +391,6 @@ class String(DType):
String
"""

__slots__ = ()


class Boolean(DType):
"""Boolean type.
Expand All @@ -420,8 +403,6 @@ class Boolean(DType):
Boolean
"""

__slots__ = ()


class Object(DType):
"""Data type for wrapping arbitrary Python objects.
Expand All @@ -435,8 +416,6 @@ class Object(DType):
Object
"""

__slots__ = ()


class Unknown(DType):
"""Type representing DataType values that could not be determined statically.
Expand All @@ -449,10 +428,8 @@ class Unknown(DType):
Unknown
"""

__slots__ = ()


class _DatetimeMeta(type):
class _DatetimeMeta(DTypeClass):
@property
def time_unit(cls) -> TimeUnit:
"""Unit of time. Defaults to `'us'` (microseconds)."""
Expand Down Expand Up @@ -546,7 +523,7 @@ def __repr__(self) -> str: # pragma: no cover
return f"{class_name}(time_unit={self.time_unit!r}, time_zone={self.time_zone!r})"


class _DurationMeta(type):
class _DurationMeta(DTypeClass):
@property
def time_unit(cls) -> TimeUnit:
"""Unit of time. Defaults to `'us'` (microseconds)."""
Expand Down Expand Up @@ -627,8 +604,6 @@ class Categorical(DType):
Categorical
"""

__slots__ = ()


class Enum(DType):
"""A fixed categorical encoding of a unique set of strings.
Expand Down Expand Up @@ -686,7 +661,7 @@ def __eq__(self, other: DType | type[DType]) -> bool: # type: ignore[override]
>>> nw.Enum(["a", "b", "c"]) == nw.Enum
True
"""
if type(other) is type:
if type(other) is DTypeClass:
return other is Enum
return isinstance(other, type(self)) and self.categories == other.categories

Expand Down Expand Up @@ -801,7 +776,7 @@ def __eq__(self, other: DType | type[DType]) -> bool: # type: ignore[override]
>>> nw.Struct({"a": nw.Int64}) == nw.Struct
True
"""
if type(other) is type and issubclass(other, self.__class__):
if type(other) is DTypeClass and issubclass(other, self.__class__):
return True
if isinstance(other, self.__class__):
return self.fields == other.fields
Expand Down Expand Up @@ -864,7 +839,7 @@ def __eq__(self, other: DType | type[DType]) -> bool: # type: ignore[override]
>>> nw.List(nw.Int64) == nw.List
True
"""
if type(other) is type and issubclass(other, self.__class__):
if type(other) is DTypeClass and issubclass(other, self.__class__):
return True
if isinstance(other, self.__class__):
return self.inner == other.inner
Expand Down Expand Up @@ -937,7 +912,7 @@ def __eq__(self, other: DType | type[DType]) -> bool: # type: ignore[override]
>>> nw.Array(nw.Int64, 2) == nw.Array
True
"""
if type(other) is type and issubclass(other, self.__class__):
if type(other) is DTypeClass and issubclass(other, self.__class__):
return True
if isinstance(other, self.__class__):
if self.shape != other.shape:
Expand Down Expand Up @@ -972,8 +947,6 @@ class Date(TemporalType):
Date
"""

__slots__ = ()


class Time(TemporalType):
"""Data type representing the time of day.
Expand All @@ -999,8 +972,6 @@ class Time(TemporalType):
Time
"""

__slots__ = ()


class Binary(DType):
"""Binary type.
Expand All @@ -1024,5 +995,3 @@ class Binary(DType):
>>> nw.from_native(rel).collect_schema()["t"]
Binary
"""

__slots__ = ()
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