Fix python implementation of IncSubtensor

pytensor/tensor/subtensor.py

@@ -1740,41 +1740,30 @@ class IncSubtensor(COp):
     def decl_view(self):
         return "PyArrayObject * zview = NULL;"
 
-    def perform(self, node, inputs, out_):
-        (out,) = out_
-        x, y = inputs[:2]
-        indices = list(reversed(inputs[2:]))
-
-        def _convert(entry):
-            if isinstance(entry, Type):
-                return indices.pop()
-            elif isinstance(entry, slice):
-                return slice(
-                    _convert(entry.start), _convert(entry.stop), _convert(entry.step)
+    def perform(self, node, inputs, output_storage):
+        x, y, *flat_indices = inputs
+
+        flat_indices_iterator = iter(flat_indices)
+        indices = tuple(
+            (
+                next(flat_indices_iterator)
+                if isinstance(entry, Type)
+                else slice(
+                    None if entry.start is None else next(flat_indices_iterator),
+                    None if entry.stop is None else next(flat_indices_iterator),
+                    None if entry.step is None else next(flat_indices_iterator),
                 )
-            else:
-                return entry
+            )
+            for entry in self.idx_list
+        )
 
-        cdata = tuple(map(_convert, self.idx_list))
-        if len(cdata) == 1:
-            cdata = cdata[0]
         if not self.inplace:
             x = x.copy()
-        sub_x = x.__getitem__(cdata)
-        if sub_x.shape:
-            # we've sliced out an N-D tensor with N > 0
-            if not self.set_instead_of_inc:
-                sub_x += y
-            else:
-                # sub_x += -sub_x + y
-                x.__setitem__(cdata, y)
+        if self.set_instead_of_inc:
+            x[indices] = y
         else:
-            # scalar case
-            if not self.set_instead_of_inc:
-                x.__setitem__(cdata, sub_x + y)
-            else:
-                x.__setitem__(cdata, y)
-        out[0] = x
+            x[indices] += y
+        output_storage[0][0] = x
 
     def c_code(self, node, name, inputs, outputs, sub):
         # This method delegates much of the work to helper