fix dtype repr and stream pass-through

cuda_py/cuda/py/_memoryview.pyx

@@ -29,7 +29,7 @@ cdef class GPUMemoryView:
         return (f"GPUMemoryView(ptr={self.ptr},\n"
               + f"              shape={self.shape},\n"
               + f"              strides={self.strides},\n"
-              + f"              dtype={get_simple_repr(numpy.dtype(self.dtype))},\n"
+              + f"              dtype={self.dtype.__name__},\n"
               + f"              device_id={self.device_id},\n"
               + f"              device_accessible={self.device_accessible},\n"
               + f"              readonly={self.readonly},\n"
@@ -39,7 +39,7 @@ cdef class GPUMemoryView:
 cdef str get_simple_repr(obj):
     cdef object obj_class = obj.__class__
     cdef str obj_repr
-    if obj_class.__module__ in (None, "__builtin__"):
+    if obj_class.__module__ in (None, "builtins"):
         obj_repr = obj_class.__name__
     else:
         obj_repr = f"{obj_class.__module__}.{obj_class.__name__}"
@@ -78,17 +78,24 @@ cdef GPUMemoryView view_as_dlpack(obj, stream_ptr):
     if dldevice == _kDLCPU:
         device_accessible = False
         assert device_id == 0
-        stream_ptr = None
+        if stream_ptr is None:
+            raise BufferError("stream=None is ambiguous with view()")
+        elif stream_ptr == -1:
+            stream_ptr = None
     elif dldevice == _kDLCUDA:
         device_accessible = True
-        stream_ptr = -1
+        # no need to check other stream values, it's a pass-through
+        if stream_ptr is None:
+            raise BufferError("stream=None is ambiguous with view()")
     elif dldevice == _kDLCUDAHost:
         device_accessible = True
         assert device_id == 0
-        stream_ptr = None
+        # just do a pass-through without any checks, as pinned memory can be
+        # accessed on both host and device
     elif dldevice == _kDLCUDAManaged:
         device_accessible = True
-        stream_ptr = -1
+        # just do a pass-through without any checks, as managed memory can be
+        # accessed on both host and device
     else:
         raise BufferError("device not supported")