code: def env(var_name, default=False):
      
      try:
          value = os.environ[var_name]
          if str(value).strip().lower() in ['false', 'no', 'off' '0', 'none', 'null']:
              return None
          return value
      except:
          from traceback import format_exc
          msg = format_exc() + '\n' + "Unable to find the %s environment variable.\nUsing the value %s (the default) instead.\n" % (var_name, default)
          warnings.warn(msg)
          return default
docs: Get the environment variable or assume a default, but let the user know about the error.