question: ImportError: _XLAC.cpython: undefined symbol
context: 🐛 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.
answer: 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!