code: def _normalize(self):
      # Step 1: Normalize the chunks so that all runs of identical charsets
      # get collapsed into a single unicode string.
      chunks = []
      last_charset = None
      last_chunk = []
      for string, charset in self._chunks:
          if charset == last_charset:
              last_chunk.append(string)
          else:
              if last_charset is not None:
                  chunks.append((SPACE.join(last_chunk), last_charset))
              last_chunk = [string]
              last_charset = charset
      if last_chunk:
          chunks.append((SPACE.join(last_chunk), last_charset))
      self._chunks = chunks
  
imports: import re
  import binascii
  import email.quoprimime
  import email.base64mime
  from email.errors import HeaderParseError
  from email import charset
label_desc: Use image node_id 7 for calling the Header obj's underlying member method code with example usage: obj._normalize() without return types