1. finetune/ pretrian fp16 amp
2. finetune/ pretrain multi processing
3. ner infer
4. py3 compat

Identity is not the same thing as equality in Python.

$ python
```
>>> self_dtype = "float"
>>> self_dtype += "16"
>>> self_dtype == "float16"
True
>>> self_dtype is "float16"
False
```

ERNIE 2.0 is a continual pre-training framework for language understanding in which pre-training tasks can be incrementally built and learned through multi-task learning

 2. return seq_lens by pad_batch_data function