Add broadcast_shapes in python API (#2091)

python/src/ops.cpp

@@ -5189,4 +5189,46 @@ void init_ops(nb::module_& m) {
       Returns:
         array: The row or col contiguous output.
     )pbdoc");
+  m.def(
+      "broadcast_shapes",
+      [](const nb::args& shapes) {
+        if (shapes.size() == 0)
+          throw std::invalid_argument(
+              "[broadcast_shapes] Must provide at least one shape.");
+
+        mx::Shape result = nb::cast<mx::Shape>(shapes[0]);
+        for (size_t i = 1; i < shapes.size(); ++i) {
+          if (!nb::isinstance<mx::Shape>(shapes[i]) &&
+              !nb::isinstance<nb::tuple>(shapes[i]))
+            throw std::invalid_argument(
+                "[broadcast_shapes] Expects a sequence of shapes (tuple or list of ints).");
+          result = mx::broadcast_shapes(result, nb::cast<mx::Shape>(shapes[i]));
+        }
+
+        return nb::tuple(nb::cast(result));
+      },
+      nb::sig("def broadcast_shapes(*shapes: Sequence[int]) -> Tuple[int]"),
+      R"pbdoc(
+        Broadcast shapes.
+
+        Returns the shape that results from broadcasting the supplied array shapes
+        against each other.
+
+        Args:
+            *shapes (Sequence[int]): The shapes to broadcast.
+
+        Returns:
+            tuple: The broadcasted shape.
+
+        Raises:
+            ValueError: If the shapes cannot be broadcast.
+
+        Example:
+            >>> mx.broadcast_shapes((1,), (3, 1))
+            (3, 1)
+            >>> mx.broadcast_shapes((6, 7), (5, 6, 1), (7,))
+            (5, 6, 7)
+            >>> mx.broadcast_shapes((5, 1, 4), (1, 3, 1))
+            (5, 3, 4)
+      )pbdoc");
 }

python/tests/test_ops.py

@@ -3043,5 +3043,45 @@ class TestOps(mlx_tests.MLXTestCase):
         self.assertTrue(np.allclose(mx.rsqrt(x), 1.0 / np.sqrt(x)))
 
 
+class TestBroadcast(mlx_tests.MLXTestCase):
+    def test_broadcast_shapes(self):
+        # Basic broadcasting
+        self.assertEqual(mx.broadcast_shapes((1, 2, 3), (3,)), (1, 2, 3))
+        self.assertEqual(mx.broadcast_shapes((4, 1, 6), (5, 6)), (4, 5, 6))
+        self.assertEqual(mx.broadcast_shapes((5, 1, 4), (1, 3, 4)), (5, 3, 4))
+
+        # Multiple arguments
+        self.assertEqual(mx.broadcast_shapes((1, 1), (1, 8), (7, 1)), (7, 8))
+        self.assertEqual(
+            mx.broadcast_shapes((6, 1, 5), (1, 7, 1), (6, 7, 5)), (6, 7, 5)
+        )
+
+        # Same shapes
+        self.assertEqual(mx.broadcast_shapes((3, 4, 5), (3, 4, 5)), (3, 4, 5))
+
+        # Single argument
+        self.assertEqual(mx.broadcast_shapes((2, 3)), (2, 3))
+
+        # Empty shapes
+        self.assertEqual(mx.broadcast_shapes((), ()), ())
+        self.assertEqual(mx.broadcast_shapes((), (1,)), (1,))
+        self.assertEqual(mx.broadcast_shapes((1,), ()), (1,))
+
+        # Broadcasting with zeroes
+        self.assertEqual(mx.broadcast_shapes((0,), (0,)), (0,))
+        self.assertEqual(mx.broadcast_shapes((1, 0, 5), (3, 1, 5)), (3, 0, 5))
+        self.assertEqual(mx.broadcast_shapes((5, 0), (0, 5, 0)), (0, 5, 0))
+
+        # Error cases
+        with self.assertRaises(ValueError):
+            mx.broadcast_shapes((3, 4), (4, 3))
+
+        with self.assertRaises(ValueError):
+            mx.broadcast_shapes((2, 3, 4), (2, 5, 4))
+
+        with self.assertRaises(ValueError):
+            mx.broadcast_shapes()
+
+
 if __name__ == "__main__":
     unittest.main()