src/transformers/models/biogpt/convert_biogpt_original_pytorch_checkpoint_to_pytorch.py/Dictionary/__init__
class Dictionary:    def __init__(
        self,
        *,  # begin keyword-only arguments
        bos="<s>",
        pad="<pad>",
        eos="</s>",
        unk="<unk>",
        extra_special_symbols=None,
    ):
        self.bos_word, self.unk_word, self.pad_word, self.eos_word = bos, unk, pad, eos
        self.symbols = []
        self.count = []
        self.indices = {}
        self.bos_index = self.add_symbol(bos)
        self.pad_index = self.add_symbol(pad)
        self.eos_index = self.add_symbol(eos)
        self.unk_index = self.add_symbol(unk)
        if extra_special_symbols:
            for s in extra_special_symbols:
                self.add_symbol(s)
        self.nspecial = len(self.symbols)