ENH: pad: pad_width can be any sequence (data-apis#114)

Author: crusaderky

src/array_api_extra/_delegation.py

@@ -1,5 +1,6 @@
 """Delegation to existing implementations for Public API Functions."""
 
+from collections.abc import Sequence
 from types import ModuleType
 from typing import Literal
 
@@ -31,7 +32,7 @@ def _delegate(xp: ModuleType, *backends: Backend) -> bool:
 
 def pad(
     x: Array,
-    pad_width: int | tuple[int, int] | list[tuple[int, int]],
+    pad_width: int | tuple[int, int] | Sequence[tuple[int, int]],
     mode: Literal["constant"] = "constant",
     *,
     constant_values: bool | int | float | complex = 0,
@@ -44,9 +45,9 @@ def pad(
     ----------
     x : array
         Input array.
-    pad_width : int or tuple of ints or list of pairs of ints
+    pad_width : int or tuple of ints or sequence of pairs of ints
         Pad the input array with this many elements from each side.
-        If a list of tuples, ``[(before_0, after_0), ... (before_N, after_N)]``,
+        If a sequence of tuples, ``[(before_0, after_0), ... (before_N, after_N)]``,
         each pair applies to the corresponding axis of ``x``.
         A single tuple, ``(before, after)``, is equivalent to a list of ``x.ndim``
         copies of this tuple.

src/array_api_extra/_lib/_funcs.py

@@ -5,6 +5,7 @@
 
 import math
 import warnings
+from collections.abc import Sequence
 from types import ModuleType
 from typing import cast
 
@@ -448,23 +449,30 @@ def nunique(x: Array, /, *, xp: ModuleType | None = None) -> Array:
 
 def pad(
     x: Array,
-    pad_width: int | tuple[int, int] | list[tuple[int, int]],
+    pad_width: int | tuple[int, int] | Sequence[tuple[int, int]],
     *,
     constant_values: bool | int | float | complex = 0,
     xp: ModuleType,
 ) -> Array:  # numpydoc ignore=PR01,RT01
     """See docstring in `array_api_extra._delegation.py`."""
     # make pad_width a list of length-2 tuples of ints
     x_ndim = cast(int, x.ndim)
+
     if isinstance(pad_width, int):
-        pad_width = [(pad_width, pad_width)] * x_ndim
-    if isinstance(pad_width, tuple):
-        pad_width = [pad_width] * x_ndim
+        pad_width_seq = [(pad_width, pad_width)] * x_ndim
+    elif (
+        isinstance(pad_width, tuple)
+        and len(pad_width) == 2
+        and all(isinstance(i, int) for i in pad_width)
+    ):
+        pad_width_seq = [cast(tuple[int, int], pad_width)] * x_ndim
+    else:
+        pad_width_seq = cast(list[tuple[int, int]], list(pad_width))
 
     # https://github.com/python/typeshed/issues/13376
     slices: list[slice] = []  # type: ignore[no-any-explicit]
     newshape: list[int] = []
-    for ax, w_tpl in enumerate(pad_width):
+    for ax, w_tpl in enumerate(pad_width_seq):
         if len(w_tpl) != 2:
             msg = f"expect a 2-tuple (before, after), got {w_tpl}."
             raise ValueError(msg)

tests/test_funcs.py

@@ -390,12 +390,12 @@ def test_tuple_width(self, xp: ModuleType):
         with pytest.raises((ValueError, RuntimeError)):
             pad(a, [(1, 2, 3)])  # type: ignore[list-item]  # pyright: ignore[reportArgumentType]
 
-    def test_list_of_tuples_width(self, xp: ModuleType):
+    def test_sequence_of_tuples_width(self, xp: ModuleType):
         a = xp.reshape(xp.arange(12), (3, 4))
-        padded = pad(a, [(1, 0), (0, 2)])
-        assert padded.shape == (4, 6)
 
-        padded = pad(a, [(1, 0), (0, 0)])
+        padded = pad(a, ((1, 0), (0, 2)))
+        assert padded.shape == (4, 6)
+        padded = pad(a, ((1, 0), (0, 0)))
         assert padded.shape == (4, 4)