API: make construct_array_type non-classmethod (#62060)

Co-authored-by: Matthew Roeschke <[email protected]>

Author: jbrockmendel

doc/source/whatsnew/v3.0.0.rst

@@ -418,6 +418,7 @@ Other API changes
   an empty ``RangeIndex`` or empty ``Index`` with object dtype when determining
   the dtype of the resulting Index (:issue:`60797`)
 - :class:`IncompatibleFrequency` now subclasses ``TypeError`` instead of ``ValueError``. As a result, joins with mismatched frequencies now cast to object like other non-comparable joins, and arithmetic with indexes with mismatched frequencies align (:issue:`55782`)
+- :meth:`ExtensionDtype.construct_array_type` is now a regular method instead of a ``classmethod`` (:issue:`58663`)
 - Comparison operations between :class:`Index` and :class:`Series` now consistently return :class:`Series` regardless of which object is on the left or right (:issue:`36759`)
 - Numpy functions like ``np.isinf`` that return a bool dtype when called on a :class:`Index` object now return a bool-dtype :class:`Index` instead of ``np.ndarray`` (:issue:`52676`)
 

pandas/core/arrays/boolean.py

@@ -85,8 +85,7 @@ def kind(self) -> str:
     def numpy_dtype(self) -> np.dtype:
         return np.dtype("bool")
 
-    @classmethod
-    def construct_array_type(cls) -> type_t[BooleanArray]:
+    def construct_array_type(self) -> type_t[BooleanArray]:
         """
         Return the array type associated with this dtype.
 

pandas/core/arrays/floating.py

@@ -28,8 +28,7 @@ class FloatingDtype(NumericDtype):
     _default_np_dtype = np.dtype(np.float64)
     _checker = is_float_dtype
 
-    @classmethod
-    def construct_array_type(cls) -> type[FloatingArray]:
+    def construct_array_type(self) -> type[FloatingArray]:
         """
         Return the array type associated with this dtype.
 

pandas/core/arrays/integer.py

@@ -28,8 +28,7 @@ class IntegerDtype(NumericDtype):
     _default_np_dtype = np.dtype(np.int64)
     _checker = is_integer_dtype
 
-    @classmethod
-    def construct_array_type(cls) -> type[IntegerArray]:
+    def construct_array_type(self) -> type[IntegerArray]:
         """
         Return the array type associated with this dtype.
 

pandas/core/arrays/numeric.py

@@ -150,7 +150,7 @@ def _coerce_to_data_and_mask(
     if dtype is not None:
         dtype = dtype_cls._standardize_dtype(dtype)
 
-    cls = dtype_cls.construct_array_type()
+    cls = dtype_cls().construct_array_type()
     if isinstance(values, cls):
         values, mask = values._data, values._mask
         if dtype is not None:

pandas/core/arrays/string_.py

@@ -283,12 +283,7 @@ def construct_from_string(cls, string) -> Self:
         else:
             raise TypeError(f"Cannot construct a '{cls.__name__}' from '{string}'")
 
-    # https://github.com/pandas-dev/pandas/issues/36126
-    # error: Signature of "construct_array_type" incompatible with supertype
-    # "ExtensionDtype"
-    def construct_array_type(  # type: ignore[override]
-        self,
-    ) -> type_t[BaseStringArray]:
+    def construct_array_type(self) -> type_t[BaseStringArray]:
         """
         Return the array type associated with this dtype.
 

pandas/core/dtypes/base.py

@@ -211,16 +211,15 @@ def names(self) -> list[str] | None:
         """
         return None
 
-    @classmethod
-    def construct_array_type(cls) -> type_t[ExtensionArray]:
+    def construct_array_type(self) -> type_t[ExtensionArray]:
         """
         Return the array type associated with this dtype.
 
         Returns
         -------
         type
         """
-        raise AbstractMethodError(cls)
+        raise AbstractMethodError(self)
 
     def empty(self, shape: Shape) -> ExtensionArray:
         """

pandas/core/dtypes/dtypes.py

@@ -527,8 +527,7 @@ def _hash_categories(self) -> int:
         combined_hashed = combine_hash_arrays(iter(cat_array), num_items=len(cat_array))
         return np.bitwise_xor.reduce(combined_hashed)
 
-    @classmethod
-    def construct_array_type(cls) -> type_t[Categorical]:
+    def construct_array_type(self) -> type_t[Categorical]:
         """
         Return the array type associated with this dtype.
 
@@ -856,8 +855,7 @@ def tz(self) -> tzinfo:
         """
         return self._tz
 
-    @classmethod
-    def construct_array_type(cls) -> type_t[DatetimeArray]:
+    def construct_array_type(self) -> type_t[DatetimeArray]:
         """
         Return the array type associated with this dtype.
 
@@ -1174,8 +1172,7 @@ def is_dtype(cls, dtype: object) -> bool:
                 return False
         return super().is_dtype(dtype)
 
-    @classmethod
-    def construct_array_type(cls) -> type_t[PeriodArray]:
+    def construct_array_type(self) -> type_t[PeriodArray]:
         """
         Return the array type associated with this dtype.
 
@@ -1363,8 +1360,7 @@ def subtype(self):
         """
         return self._subtype
 
-    @classmethod
-    def construct_array_type(cls) -> type[IntervalArray]:
+    def construct_array_type(self) -> type[IntervalArray]:
         """
         Return the array type associated with this dtype.
 
@@ -1576,8 +1572,7 @@ def construct_from_string(cls, string: str) -> NumpyEADtype:
             raise TypeError(msg) from err
         return cls(dtype)
 
-    @classmethod
-    def construct_array_type(cls) -> type_t[NumpyExtensionArray]:
+    def construct_array_type(self) -> type_t[NumpyExtensionArray]:
         """
         Return the array type associated with this dtype.
 
@@ -1649,8 +1644,7 @@ def itemsize(self) -> int:
         """Return the number of bytes in this dtype"""
         return self.numpy_dtype.itemsize
 
-    @classmethod
-    def construct_array_type(cls) -> type_t[BaseMaskedArray]:
+    def construct_array_type(self) -> type_t[BaseMaskedArray]:
         """
         Return the array type associated with this dtype.
 
@@ -1914,8 +1908,7 @@ def name(self) -> str:
     def __repr__(self) -> str:
         return self.name
 
-    @classmethod
-    def construct_array_type(cls) -> type_t[SparseArray]:
+    def construct_array_type(self) -> type_t[SparseArray]:
         """
         Return the array type associated with this dtype.
 
@@ -2316,8 +2309,7 @@ def itemsize(self) -> int:
         """Return the number of bytes in this dtype"""
         return self.numpy_dtype.itemsize
 
-    @classmethod
-    def construct_array_type(cls) -> type_t[ArrowExtensionArray]:
+    def construct_array_type(self) -> type_t[ArrowExtensionArray]:
         """
         Return the array type associated with this dtype.
 

pandas/tests/arrays/test_array.py

@@ -487,8 +487,7 @@ def test_bounds_check():
 class DecimalDtype2(DecimalDtype):
     name = "decimal2"
 
-    @classmethod
-    def construct_array_type(cls):
+    def construct_array_type(self):
         """
         Return the array type associated with this dtype.
 

pandas/tests/dtypes/test_common.py

@@ -576,8 +576,7 @@ def type(self):
         def name(self):
             raise NotImplementedError
 
-        @classmethod
-        def construct_array_type(cls):
+        def construct_array_type(self):
             raise NotImplementedError
 
         def _is_numeric(self) -> bool: