From 81db5e5e5b5cbe63d820f80c70f9781109beb6be Mon Sep 17 00:00:00 2001
From: Oleksandr Pavlyk <21087696+oleksandr-pavlyk@users.noreply.github.com>
Date: Mon, 13 Jan 2025 11:00:53 -0600
Subject: [PATCH] Implement usm_ndarray.__arrray__ method

The property raises TypeError informing user that
implicit conversions from usm_ndarray to numpy.ndarray
are not permitted.

Explicit conversion using `dpctl.tensor.asnumpy` is
advised.

Disallowing implicit conversion prevents `np.asarray(usm_ar)`
from creating an array of 0D usm_ndarray instances, because
using it is very costly due to multitude of short-array transfers
from GPU to host.
---
 dpctl/tensor/_usmarray.pyx | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/dpctl/tensor/_usmarray.pyx b/dpctl/tensor/_usmarray.pyx
index f61651d4b3..150f0b3b65 100644
--- a/dpctl/tensor/_usmarray.pyx
+++ b/dpctl/tensor/_usmarray.pyx
@@ -1552,6 +1552,14 @@ cdef class usm_ndarray:
     def __repr__(self):
         return usm_ndarray_repr(self)
 
+    def __array__(self, dtype=None, copy=None):
+        "NumPy array protocol"
+        raise TypeError(
+            "Implicit conversion to a NumPy array is not allowed. "
+	    "Use `dpctl.tensor.asnumpy` to copy data from this "
+	    "`dpctl.tensor.usm_ndarray` instance to NumPy array"
+	)
+
 
 cdef usm_ndarray _real_view(usm_ndarray ary):
     """