review

Author: crusaderky

array_api_compat/common/_helpers.py

@@ -900,6 +900,8 @@ def __getitem__(self, idx):
         which looks prettier than ``at(x, slice(start, stop, step))``
         and feels more intuitive coming from the JAX documentation.
         """
+        if self.idx is not _undef:
+            raise TypeError("Index has already been set")
         self.idx = idx
         return self