numpy · mhvk · Jan 21, 2024 · Jan 11, 2024 · Jan 19, 2024 · Jan 19, 2024
diff --git a/doc/release/upcoming_changes/25570.change b/doc/release/upcoming_changes/25570.change
@@ -0,0 +1,7 @@
+Functions that returned a list of ndarrays have been changed to return a tuple
+of ndarrays instead. Returning tuples consistently whenever a sequence of
+arrays is returned makes it easier for JIT compilers like Numba, as well as for
+static type checkers in some cases, to support these functions. Changed
+functions are: ``atleast_1d``, ``atleast_2d``, ``atleast_3d``, ``broadcast_arrays``,
+``array_split``, ``split``, ``hsplit``, ``vsplit``, ``dsplit``, ``meshgrid``,
+``ogrid``, ``histogramdd``.
diff --git a/numpy/_core/shape_base.py b/numpy/_core/shape_base.py
@@ -36,7 +36,7 @@ def atleast_1d(*arys):
     Returns
     -------
     ret : ndarray
-        An array, or list of arrays, each with ``a.ndim >= 1``.
+        An array, or tuple of arrays, each with ``a.ndim >= 1``.
         Copies are made only if necessary.
 
     See Also
@@ -57,7 +57,7 @@ def atleast_1d(*arys):
     True
 
     >>> np.atleast_1d(1, [3, 4])
-    [array([1]), array([3, 4])]
+    (array([1]), array([3, 4]))
 
     """
     res = []
@@ -71,7 +71,7 @@ def atleast_1d(*arys):
     if len(res) == 1:
         return res[0]
     else:
-        return res
+        return tuple(res)
 
 
 def _atleast_2d_dispatcher(*arys):
@@ -93,7 +93,7 @@ def atleast_2d(*arys):
     Returns
     -------
     res, res2, ... : ndarray
-        An array, or list of arrays, each with ``a.ndim >= 2``.
+        An array, or tuple of arrays, each with ``a.ndim >= 2``.
         Copies are avoided where possible, and views with two or more
         dimensions are returned.
 
@@ -113,7 +113,7 @@ def atleast_2d(*arys):
     True
 
     >>> np.atleast_2d(1, [1, 2], [[1, 2]])
-    [array([[1]]), array([[1, 2]]), array([[1, 2]])]
+    (array([[1]]), array([[1, 2]]), array([[1, 2]]))
 
     """
     res = []
@@ -129,7 +129,7 @@ def atleast_2d(*arys):
     if len(res) == 1:
         return res[0]
     else:
-        return res
+        return tuple(res)
 
 
 def _atleast_3d_dispatcher(*arys):
@@ -151,7 +151,7 @@ def atleast_3d(*arys):
     Returns
     -------
     res1, res2, ... : ndarray
-        An array, or list of arrays, each with ``a.ndim >= 3``.  Copies are
+        An array, or tuple of arrays, each with ``a.ndim >= 3``.  Copies are
         avoided where possible, and views with three or more dimensions are
         returned.  For example, a 1-D array of shape ``(N,)`` becomes a view
         of shape ``(1, N, 1)``, and a 2-D array of shape ``(M, N)`` becomes a
@@ -201,7 +201,7 @@ def atleast_3d(*arys):
     if len(res) == 1:
         return res[0]
     else:
-        return res
+        return tuple(res)
 
 
 def _arrays_for_stack_dispatcher(arrays):
@@ -282,8 +282,8 @@ def vstack(tup, *, dtype=None, casting="same_kind"):
 
     """
     arrs = atleast_2d(*tup)
-    if not isinstance(arrs, list):
-        arrs = [arrs]
+    if not isinstance(arrs, tuple):
+        arrs = (arrs,)
     return _nx.concatenate(arrs, 0, dtype=dtype, casting=casting)
 
 
@@ -349,8 +349,8 @@ def hstack(tup, *, dtype=None, casting="same_kind"):
 
     """
     arrs = atleast_1d(*tup)
-    if not isinstance(arrs, list):
-        arrs = [arrs]
+    if not isinstance(arrs, tuple):
+        arrs = (arrs,)
     # As a special case, dimension 0 of 1-dimensional arrays is "horizontal"
     if arrs and arrs[0].ndim == 1:
         return _nx.concatenate(arrs, 0, dtype=dtype, casting=casting)

diff --git a/numpy/_core/shape_base.pyi b/numpy/_core/shape_base.pyi
@@ -20,21 +20,21 @@ def atleast_1d(arys: _ArrayLike[_SCT], /) -> NDArray[_SCT]: ...
 @overload
 def atleast_1d(arys: ArrayLike, /) -> NDArray[Any]: ...
 @overload
-def atleast_1d(*arys: ArrayLike) -> list[NDArray[Any]]: ...
+def atleast_1d(*arys: ArrayLike) -> tuple[NDArray[Any], ...]: ...
 
 @overload
 def atleast_2d(arys: _ArrayLike[_SCT], /) -> NDArray[_SCT]: ...
 @overload
 def atleast_2d(arys: ArrayLike, /) -> NDArray[Any]: ...
 @overload
-def atleast_2d(*arys: ArrayLike) -> list[NDArray[Any]]: ...
+def atleast_2d(*arys: ArrayLike) -> tuple[NDArray[Any], ...]: ...
 
 @overload
 def atleast_3d(arys: _ArrayLike[_SCT], /) -> NDArray[_SCT]: ...
 @overload
 def atleast_3d(arys: ArrayLike, /) -> NDArray[Any]: ...
 @overload
-def atleast_3d(*arys: ArrayLike) -> list[NDArray[Any]]: ...
+def atleast_3d(*arys: ArrayLike) -> tuple[NDArray[Any], ...]: ...
 
 @overload
 def vstack(

diff --git a/numpy/lib/_function_base_impl.py b/numpy/lib/_function_base_impl.py
@@ -4986,7 +4986,7 @@ def _meshgrid_dispatcher(*xi, copy=None, sparse=None, indexing=None):
 @array_function_dispatch(_meshgrid_dispatcher)
 def meshgrid(*xi, copy=True, sparse=False, indexing='xy'):
     """
-    Return a list of coordinate matrices from coordinate vectors.
+    Return a tuple of coordinate matrices from coordinate vectors.
 
     Make N-D coordinate arrays for vectorized evaluations of
     N-D scalar/vector fields over N-D grids, given
@@ -5027,7 +5027,7 @@ def meshgrid(*xi, copy=True, sparse=False, indexing='xy'):
 
     Returns
     -------
-    X1, X2,..., XN : list of ndarrays
+    X1, X2,..., XN : tuple of ndarrays
         For vectors `x1`, `x2`,..., `xn` with lengths ``Ni=len(xi)``,
         returns ``(N1, N2, N3,..., Nn)`` shaped arrays if indexing='ij'
         or ``(N2, N1, N3,..., Nn)`` shaped arrays if indexing='xy'
@@ -5136,7 +5136,7 @@ def meshgrid(*xi, copy=True, sparse=False, indexing='xy'):
         output = np.broadcast_arrays(*output, subok=True)
 
     if copy:
-        output = [x.copy() for x in output]
+        output = tuple(x.copy() for x in output)
 
     return output
 

diff --git a/numpy/lib/_function_base_impl.pyi b/numpy/lib/_function_base_impl.pyi
@@ -626,7 +626,7 @@ def meshgrid(
     copy: bool = ...,
     sparse: bool = ...,
     indexing: L["xy", "ij"] = ...,
-) -> list[NDArray[Any]]: ...
+) -> tuple[NDArray[Any], ...]: ...
 
 @overload
 def delete(

diff --git a/numpy/lib/_histograms_impl.py b/numpy/lib/_histograms_impl.py
@@ -957,8 +957,8 @@ def histogramdd(sample, bins=10, range=None, density=None, weights=None):
     H : ndarray
         The multidimensional histogram of sample x. See density and weights
         for the different possible semantics.
-    edges : list
-        A list of D arrays describing the bin edges for each dimension.
+    edges : tuple of ndarrays
+        A tuple of D arrays describing the bin edges for each dimension.
 
     See Also
     --------

diff --git a/numpy/lib/_histograms_impl.pyi b/numpy/lib/_histograms_impl.pyi
@@ -44,4 +44,4 @@ def histogramdd(
     range: Sequence[tuple[float, float]] = ...,
     density: None | bool = ...,
     weights: None | ArrayLike = ...,
-) -> tuple[NDArray[Any], list[NDArray[Any]]]: ...
+) -> tuple[NDArray[Any], tuple[NDArray[Any], ...]]: ...
diff --git a/numpy/lib/_index_tricks_impl.py b/numpy/lib/_index_tricks_impl.py
@@ -189,7 +189,8 @@ def __getitem__(self, key):
                     slobj[k] = slice(None, None)
                     nn[k] = nn[k][tuple(slobj)]
                     slobj[k] = _nx.newaxis
-            return nn
+                return tuple(nn)  # ogrid -> tuple of arrays
+            return nn  # mgrid -> ndarray
         except (IndexError, TypeError):
             step = key.step
             stop = key.stop
@@ -225,8 +226,9 @@ class MGridClass(nd_grid):
 
     Returns
     -------
-    mesh-grid
-        `ndarray`\\ s all of the same dimensions
+    mesh-grid : ndarray
+        A single array, containing a set of `ndarray`\\ s all of the same
+        dimensions. stacked along the first axis.
 
     See Also
     --------
@@ -251,6 +253,13 @@ class MGridClass(nd_grid):
     >>> np.mgrid[-1:1:5j]
     array([-1. , -0.5,  0. ,  0.5,  1. ])
 
+    >>> np.mgrid[0:4].shape
+    (4,)
+    >>> np.mgrid[0:4, 0:5].shape
+    (2, 4, 5)
+    >>> np.mgrid[0:4, 0:5, 0:6].shape
+    (3, 4, 5, 6)
+
     """
 
     def __init__(self):
@@ -277,8 +286,10 @@ class OGridClass(nd_grid):
 
     Returns
     -------
-    mesh-grid
-        `ndarray`\\ s with only one dimension not equal to 1
+    mesh-grid : ndarray or tuple of ndarrays
+        If the input is a single slice, returns an array.
+        If the input is multiple slices, returns a tuple of arrays, with
+        only one dimension not equal to 1.
 
     See Also
     --------
@@ -292,12 +303,13 @@ class OGridClass(nd_grid):
     >>> from numpy import ogrid
     >>> ogrid[-1:1:5j]
     array([-1. , -0.5,  0. ,  0.5,  1. ])
-    >>> ogrid[0:5,0:5]
-    [array([[0],
+    >>> ogrid[0:5, 0:5]
+    (array([[0],
             [1],
             [2],
             [3],
-            [4]]), array([[0, 1, 2, 3, 4]])]
+            [4]]),
+     array([[0, 1, 2, 3, 4]]))
 
     """
 

diff --git a/numpy/lib/_index_tricks_impl.pyi b/numpy/lib/_index_tricks_impl.pyi
@@ -74,7 +74,7 @@ class nd_grid(Generic[_BoolType]):
     def __getitem__(
         self: nd_grid[Literal[True]],
         key: slice | Sequence[slice],
-    ) -> list[NDArray[Any]]: ...
+    ) -> tuple[NDArray[Any], ...]: ...
 
 class MGridClass(nd_grid[Literal[False]]):
     def __init__(self) -> None: ...