code: def __new__(cls, key, default_value):
      if key in ContextVar._cache:
          return ContextVar._cache[key]
      instance = ContextVar._cache[key] = super().__new__(cls)
      instance.value = getenv(key, default_value)
      return instance
  
imports: from __future__ import annotations
  import os, functools, platform, time, re, contextlib, operator, hashlib, pickle, sqlite3, cProfile, pstats, tempfile, pathlib, string, ctypes
  from urllib import request
  from tqdm import tqdm
  from typing import Dict, Tuple, Union, List, ClassVar, Optional, Iterable, Any, TypeVar, TYPE_CHECKING, Callable, Sequence
label_desc: Use image node_id 1 for calling the ContextVar obj's underlying member method code with example usage: obj.__new__(cls, key, default_value) and returns: instance, ContextVar