AttributeError: module 'taichi' has no attribute 'ext_arr'

Dear team,
when I run the example in "toy" folder, I got errors as below,
```
if attr == "cfg":
     21     return None if lang.impl.get_runtime().prog is None else lang.impl.current_cfg()
---> 22 raise AttributeError(f"module '{__name__}' has no attribute '{attr}'")

AttributeError: module 'taichi' has no attribute 'ext_arr'
```
Is there suggestion to fix this issue? Thanks.