class_docstr: A cache structure that maps style strings to :class:`.Attr`.
  (This is an important speed up.)
class_docstr_tok: ["A","cache","structure","that","maps","style","strings","to",":","class",":","`",".Attr","`",".","(","This","is","an","important","speed","up",".",")"]
code: def __missing__(self, style_str: str) -> Attrs:
      attrs = self.get_attrs_for_style_str(style_str)
      attrs = self.style_transformation.transform_attrs(attrs)
  
      self[style_str] = attrs
      return attrs
  
imports: from __future__ import annotations
  from asyncio import FIRST_COMPLETED, Future, ensure_future, sleep, wait
  from collections import deque
  from enum import Enum
  from typing import TYPE_CHECKING, Any, Callable, Dict, Hashable
  from prompt_toolkit.application.current import get_app
  from prompt_toolkit.cursor_shapes import CursorShape
  from prompt_toolkit.data_structures import Point, Size
  from prompt_toolkit.filters import FilterOrBool, to_filter
  from prompt_toolkit.formatted_text import AnyFormattedText, to_formatted_text
  from prompt_toolkit.layout.mouse_handlers import MouseHandlers
  from prompt_toolkit.layout.screen import Char, Screen, WritePosition
  from prompt_toolkit.output import ColorDepth, Output
  from prompt_toolkit.styles import Attrs, BaseStyle, DummyStyleTransformation, StyleTransformation
label_desc: Use image node_id 2 for calling the _StyleStringToAttrsCache obj's underlying member method code with example usage: obj.__missing__(style_str) and returns: attrs