docstr: Add prefix to label words. For example, if a label words is in the middle of a template,
  the prefix should be ``' '``.
  
  Args:
      label_words (:obj:`Union[Sequence[str], Mapping[str, str]]`, optional): The label words that are projected by the labels.
      prefix (:obj:`str`, optional): The prefix string of the verbalizer.
  
  Returns:
      :obj:`Sequence[str]`: New label words with prefix.
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code: def add_prefix(label_words, prefix):
      r"""Add prefix to label words. For example, if a label words is in the middle of a template,
      the prefix should be ``' '``.
  
      Args:
          label_words (:obj:`Union[Sequence[str], Mapping[str, str]]`, optional): The label words that are projected by the labels.
          prefix (:obj:`str`, optional): The prefix string of the verbalizer.
  
      Returns:
          :obj:`Sequence[str]`: New label words with prefix.
      """
      new_label_words = []
      if isinstance(label_words[0], str):
          label_words = [
              [w] for w in label_words
          ]  # wrapped it to a list of list of label words.
  
      for label_words_per_label in label_words:
          new_label_words_per_label = []
          for word in label_words_per_label:
              if word.startswith("<!>"):
                  new_label_words_per_label.append(word.split("<!>")[1])
              else:
                  new_label_words_per_label.append(prefix + word)
          new_label_words.append(new_label_words_per_label)
      return new_label_words
  
imports: import paddle
  from abc import abstractmethod
  from typing import *
  import numpy
  import paddle.nn.functional
label_desc: Use image node_id 3 for calling the ErnieManualVerbalizer obj's underlying member method code with example usage: obj.add_prefix(label_words, prefix) and returns: new_label_words