ImportError: _XLAC.cpython: undefined symbol
🐛 Bug

Import error after installing pytorch-lightning on google colab TPU instance.

Colab link: https://colab.research.google.com/drive/1ssH3PwBh6skcIze440LwHn5R5dUnih7Q?usp=sharing
Code to reproduce:
!pip install cloud-tpu-client==0.10 https://storage.googleapis.com/tpu-pytorch/wheels/torch_xla-1.8-cp37-cp37m-linux_x86_64.whl
!pip install pytorch-lightning

import pytorch_lightning as pl

Console output:
WARNING:root:Waiting for TPU to be start up with version pytorch-1.8...
WARNING:root:Waiting for TPU to be start up with version pytorch-1.8...
WARNING:root:TPU has started up successfully with version pytorch-1.8
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-2-efd8697dde72> in <module>()
----> 1 import pytorch_lightning as pl

9 frames
/usr/local/lib/python3.7/dist-packages/torch_xla/__init__.py in <module>()
    126 import torch
    127 from ._patched_functions import _apply_patches
--> 128 import _XLAC
    129 
    130 

ImportError: /usr/local/lib/python3.7/dist-packages/_XLAC.cpython-37m-x86_64-linux-gnu.so: undefined symbol: _ZN2at11result_typeERKNS_6TensorEN3c106ScalarE

I followed the instructions from the docs: https://pytorch-lightning.readthedocs.io/en/stable/advanced/tpu.html. I also tried xla version 1.7, 1.6, and pl version 1.1.8.
Hi @BryanWBear, this error is raised when the PyTorch and PyTorch xla are not of the same versions.
You could verify using pip list | grep torch and could install the latest versions for both!