Transform block in Datablock overwrite each other

fastai
1

I am having trouble using my custom transform block multiple times in Datablock

Here is my transform block


def TextBlock(mode):
  if mode =='bert': 
    bert_tokenizer = BertTokenizer.from_pretrained('bert-base-uncased',max_length=20)
    tf_bert = TextTransform(bert_tokenizer, 20)
    return TransformBlock(type_tfms=tf_bert.encodes)
  elif mode =='xlnet':
    xlnet_tokenizer = XLNetTokenizer.from_pretrained('xlnet-base-cased', max_length=20)
    tf_xlnet = TextTransform(xlnet_tokenizer, 20)
    return TransformBlock(type_tfms=tf_xlnet.encodes)

Here is how I use it in my datablock:

dblock_full = DataBlock(blocks=(TextBlock(mode='bert'), TextBlock(mode='xlnet'),
                                CategoryBlock),
                    get_x= [ColReader('bert_text'),
                            ColReader('xlnet_text')],
                    get_y = ColReader('category'),
                     splitter=RandomSplitter(valid_pct=0,seed=42)
                   )

Two ColReader are reading off 2 different column ( pandas series ) here. I made sure these 2 columns are independent object ( IE: not shallow copy) .

Issue:

Whatever Transform block that comes second in the blocks tuple gets apply twice and I have both of my passed in columns transformed by the last block twice.

blocks=(TextBlock(mode=‘bert’), TextBlock(mode=‘xlnet’) produce the same effect as passing in
(TextBlock(mode=‘xlnet’), TextBlock(mode=‘xlnet’) )

And if I reverse the order and let blocks=( TextBlock(mode=‘xlnet’) , TextBlock(mode=‘bert’)) then the effect will be the same as passing in (TextBlock(mode=‘bert’), TextBlock(mode=‘bert’) )

What I am doing wrong here ?