android_ndk_api_level = prompt_loop_or_load_from_env(
      environ_cp,
      var_name='ANDROID_NDK_API_LEVEL',
      var_default='21',  # 21 is required for ARM64 support.
      ask_for_var=(
          'Please specify the (min) Android NDK API level to use. '
          '[Available levels: %s]'
      )
      % api_levels,
      check_success=(lambda *_: True),