code: def _check_available():
      if not _available:
          warnings.warn(
              "matplotlib is not installed on your environment, "
              "so nothing will be plotted at this time. "
              "Please install matplotlib to plot figures.\n\n"
              "  $ pip install matplotlib\n"
          )
  
file_path: chainercv/chainercv/extensions/vis_report/detection_vis_report.py
imports: import copy
  import os
  import warnings
  import chainer
  from chainercv.visualizations.vis_bbox import vis_bbox
label_desc: Use image node_id 1 for calling a global function with example usage: _check_available() without return types