ImportError: cannot import name 'BigBirdTokenizer' from 'transformers'
## Environment info
<!-- You can run the command `transformers-cli env` and copy-and-paste its output below.
     Don't forget to fill out the missing fields in that output! -->

- `transformers` version: 4.9.1
- Platform: windows
- Python version: 3.9
- PyTorch version (GPU?): 1.9 (CPU)
- Tensorflow version (GPU?):
- Using GPU in script?: no
- Using distributed or parallel set-up in script?:


## Information

Model I am using BigBird:

The problem arises when using:
* [ ] the official example scripts: (give details below)
* [X] my own modified scripts: (give details below)

The tasks I am working on is:
* [ ] an official GLUE/SQUaD task: (give the name)
* [x] my own task or dataset: (give details below)

## To reproduce

Steps to reproduce the behavior:
```

from transformers import BigBirdTokenizer,BigBirdModel

print("hello")

```
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## Expected behavior

No import error.
Importing **BigBirdTokenizerFast** works without a problem.
The sentencepiece library was missing. <|||||>`BigBirdTokenizer` requires a sentencepiece installation, but you should have had that error instead of an import error. This is because the `BigBirdTokenizer` was misplaced in the init, the PR linked above fixes it.<|||||>I sadly only got the import error, nothing else. An error indicating that sentencepiece is missing is definitely more helpful. Thanks for creating the PR<|||||>I installed sentencepiece but I got the same error:

```
!pip install --quiet sentencepiece
from transformers import BigBirdTokenizer
```
ImportError: cannot import name 'BigBirdTokenizer' from 'transformers' (/usr/local/lib/python3.7/dist-packages/transformers/__init__.py)<|||||>@MariamDundua what is the version of your transformers package?<|||||>Hi @zynos @sgugger . I'm using transformers 4.8.0 and have installed sentencepiece. But I'm having same cannot import name 'BigBirdTokenizer' issue. Thanks. <|||||>Make sure you use the latest version of Transformers. It should include a clearer error message if the import fails.