fix import on current apex

[esemeniuc]

Fixes the error:

Traceback (most recent call last):
  File "unilm/src/biunilm/run_seq2seq.py", line 21, in <module>
    from pytorch_pretrained_bert.tokenization import BertTokenizer, WhitespaceTokenizer
  File "/content/unilm/src/pytorch_pretrained_bert/__init__.py", line 6, in <module>
    from .optimization_fp16 import FP16_Optimizer_State
  File "/content/unilm/src/pytorch_pretrained_bert/optimization_fp16.py", line 4, in <module>
    from apex.optimizers import FP16_Optimizer
ImportError: cannot import name 'FP16_Optimizer'

[donglixp]

Thanks for the P&R. We use the following version of apex, whose APIs are quite different to the current version.

git clone -q https://github.com/NVIDIA/apex.git
cd apex
git reset --hard 1603407bf49c7fc3da74fceb6a6c7b47fece2ef8
python setup.py install --user --cuda_ext --cpp_ext

We will keep the commit here for reference.