KeyError: 'UNK'

[eman226]

def init(self, config, train_path=None, token_to_id=None,
dropout_prob=0.25, replacement_prob=0.25, dataset_copies=2):
super(MovieDialogReader, self).init(
config, train_path=train_path, token_to_id=token_to_id,
special_tokens=[
PAD_TOKEN, GO_TOKEN, EOS_TOKEN,
MovieDialogReader.UNKNOWN_TOKEN],
dataset_copies=dataset_copies)

    self.dropout_prob = dropout_prob
    self.replacement_prob = replacement_prob
    self.UNKNOWN_ID = self.token_to_id[MovieDialogReader.UNKNOWN_TOKEN]

#last line gives error
#I dont understand where UNKNOWN_ID is coming from and what token_to_id actually is

[meghamodi]

I'm getting the same error.

_File "/home/ubuntu/deep-text-corrector/text_corrector_data_readers.py", line 87, in __init__
   self.UNKNOWN_ID = self.token_to_id[MovieDialogReader.UNKNOWN_TOKEN]
KeyError: 'UNK'_