Requirements should specify pyarrow<1
I am sorry for hijacking this closed issue, but I believe I was able to reproduce this very issue. Strangely enough, it also turned out that running `pip install "pyarrow<1" --upgrade` did indeed fix the issue (PyArrow was installed in version `0.14.1` in my case).

Please see the Colab below:

https://colab.research.google.com/drive/15QQS3xWjlKW2aK0J74eEcRFuhXUddUST

Thanks!
I was looking at the docs on [Perplexity](https://huggingface.co/transformers/perplexity.html) via GPT2. When you load datasets and try to load Wikitext, you get the error,

```
module 'pyarrow' has no attribute 'PyExtensionType'
```
I traced it back to datasets having installed PyArrow 1.0.1 but there's not pinning in the setup file. 

https://github.com/huggingface/datasets/blob/e86a2a8f869b91654e782c9133d810bb82783200/setup.py#L68

Downgrading by installing `pip install "pyarrow<1"` resolved the issue.
Requirements should specify pyarrow<1 
 I was looking at the docs on [Perplexity](https://huggingface.co/transformers/perplexity.html) via GPT2. When you load datasets and try to load Wikitext, you get the error,

```
module 'pyarrow' has no attribute 'PyExtensionType'
```
I traced it back to datasets having installed PyArrow 1.0.1 but there's not pinning in the setup file. 

https://github.com/huggingface/datasets/blob/e86a2a8f869b91654e782c9133d810bb82783200/setup.py#L68

Downgrading by installing `pip install "pyarrow<1"` resolved the issue. 
 I am sorry for hijacking this closed issue, but I believe I was able to reproduce this very issue. Strangely enough, it also turned out that running `pip install "pyarrow<1" --upgrade` did indeed fix the issue (PyArrow was installed in version `0.14.1` in my case).

Please see the Colab below:

https://colab.research.google.com/drive/15QQS3xWjlKW2aK0J74eEcRFuhXUddUST

Thanks!