Cannot read IWSLT dataset

[erlebach]

Hi,

The following code does not execute:
"""
train_data, valid_data, test_data = datasets.IWSLT.splits(
exts=('.de', '.en'), fields=(SRC, TRG),
filter_pred=lambda x: len(vars(x)['src']) <= MAX_LEN and
len(vars(x)['trg']) <= MAX_LEN
"""
What should I replace this code with? Thanks for a great code base.