class_docstr: 用于读取 **conll2003** 任务的 NER 数据。每一行有 4 列内容，空行意味着隔开两个句子。
  
  支持读取的内容如下::
  
      Nadim NNP B-NP B-PER
      Ladki NNP I-NP I-PER
  
      AL-AIN NNP B-NP B-LOC
      United NNP B-NP B-LOC
      Arab NNP I-NP I-LOC
      Emirates NNPS I-NP I-LOC
      1996-12-06 CD I-NP O
      ...
  
  读取的 :class:`~fastNLP.core.DataSet` 将具备以下的数据结构：
  
  .. csv-table:: 下面是 Conll2003Loader 加载后数据具备的结构, target 是 BIO2 编码
     :header: "raw_words", "target"
  
     "[Nadim, Ladki]", "[B-PER, I-PER]"
     "[AL-AIN, United, Arab, ...]", "[B-LOC, B-LOC, I-LOC, ...]"
     "[...]",  "[...]"
class_docstr_tok: ["\u7528\u4e8e\u8bfb\u53d6","*","*","conll2003","*","*","\u4efb\u52a1\u7684","NER","\u6570\u636e\u3002\u6bcf\u4e00\u884c\u6709","4","\u5217\u5185\u5bb9\uff0c\u7a7a\u884c\u610f\u5473\u7740\u9694\u5f00\u4e24\u4e2a\u53e5\u5b50\u3002","\u652f\u6301\u8bfb\u53d6\u7684\u5185\u5bb9\u5982\u4e0b",":",":","Nadim","NNP","B-NP","B-PER","Ladki","NNP","I-NP","I-PER","AL-AIN","NNP","B-NP","B-LOC","United","NNP","B-NP","B-LOC","Arab","NNP","I-NP","I-LOC","Emirates","NNPS","I-NP","I-LOC","1996-12-06","CD","I-NP","O","...","\u8bfb\u53d6\u7684",":","class",":","`","~fastNLP.core.DataSet","`","\u5c06\u5177\u5907\u4ee5\u4e0b\u7684\u6570\u636e\u7ed3\u6784\uff1a","..","csv-table",":",":","\u4e0b\u9762\u662f","Conll2003Loader","\u52a0\u8f7d\u540e\u6570\u636e\u5177\u5907\u7684\u7ed3\u6784",",","target","\u662f","BIO2","\u7f16\u7801",":","header",":","``","raw_words","''",",","``","target","''","``","[","Nadim",",","Ladki","]","''",",","``","[","B-PER",",","I-PER","]","''","``","[","AL-AIN",",","United",",","Arab",",","...","]","''",",","``","[","B-LOC",",","B-LOC",",","I-LOC",",","...","]","''","``","[","...","]","''",",","``","[","...","]","''"]
code: def download(self):
      raise RuntimeError(
          "conll2003 cannot be downloaded automatically."
      )
  
imports: import glob
  import os
  import random
  import shutil
  import time
  from typing import List
  from .loader import Loader
  from ..file_reader import _read_conll
  from fastNLP.core.dataset import DataSet, Instance
label_desc: Use image node_id 3 for calling the Conll2003NERLoader obj's underlying member method code with example usage: obj.download() without return types