text: from . import _base
  
  class Filter(_base.Filter):
      def __init__(self, source, encoding):
          _base.Filter.__init__(self, source)
          self.encoding = encoding
  
      def __iter__(self):
          state = "pre_head"
          meta_found = (self.encoding is None)
          pending = []
  
          for token in _base.Filter.__iter__(self):
              type = token["type"]
              if type == "StartTag":
                  if token["name"].lower() == "head":
                      state = "in_head"
  
              elif type == "EmptyTag":
                  if token["name"].lower() == "meta":
                     # replace charset with actual encoding
                     has_http_equiv_content_type = False
                     for (namespace,name),value in token["data"].items():
                         if namespace != None:
                             continue
                         elif name.lower() == 'charset':
                            token["data"][(namespace,name)] = self.encoding
                            meta_found = True
                            break
                         elif name == 'http-equiv' and value.lower() == 'content-type':
                             has_http_equiv_content_type = True
                     else:
                         if has_http_equiv_content_type and (None, "content") in token["data"]:
                             token["data"][(None, "content")] = 'text/html; charset=%s' % self.encoding
                             meta_found = True
  
                  elif token["name"].lower() == "head" and not meta_found:
                      # insert meta into empty head
                      yield {"type": "StartTag", "name": "head",
                             "data": token["data"]}
                      yield {"type": "EmptyTag", "name": "meta",
                             "data": {(None, "charset"): self.encoding}}
                      yield {"type": "EndTag", "name": "head"}
                      meta_found = True
                      continue
  
              elif type == "EndTag":
                  if token["name"].lower() == "head" and pending:
                      # insert meta into head (if necessary) and flush pending queue
                      yield pending.pop(0)
                      if not meta_found:
                          yield {"type": "EmptyTag", "name": "meta",
                                 "data": {(None, "charset"): self.encoding}}
                      while pending:
                          yield pending.pop(0)
                      meta_found = True
                      state = "post_head"
  
              if state == "in_head":
                  pending.append(token)
              else:
                  yield token
  