load_dataset from local squad.py, raise error: TypeError: 'NoneType' object is not callable 
Hi !
Thanks for reporting.
It looks like no object inherits from `datasets.GeneratorBasedBuilder` (or more generally from `datasets.DatasetBuilder`) in your script.

Could you check that there exist at least one dataset builder class ? Hi @xixiaoyao did you manage to fix your issue ? No activity, closing It happened when try to change the old project which use 'nlp' to new project which use 'datasets'. You should check you old 'my_squad.py' file, change the inherit class from `nlp.xxx` to `datasets.xxx`. Otherwise datasets - load.py - import_main_class() `if inspect.isclass(obj) and issubclass(obj, main_cls_type):` can not find the main_cls.

version: 1.0.2

```
train_dataset  = datasets.load_dataset('squad') 
```

The above code can works. However, when I download the squad.py from your server, and saved as `my_squad.py` to local. I run followings raise errors.
```
train_dataset  = datasets.load_dataset('./my_squad.py')                                                                                                
```
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-28-25a84b4d1581> in <module>
----> 1 train_dataset  = nlp.load_dataset('./my_squad.py')

/opt/conda/lib/python3.7/site-packages/datasets/load.py in load_dataset(path, name, data_dir, data_files, split, cache_dir, features, download_config, download_mode, ignore_verifications, save_infos, script_version, **config_kwargs)
    602         hash=hash,
    603         features=features,
--> 604         **config_kwargs,
    605     )
    606 

TypeError: 'NoneType' object is not callable
