code: def _check_available():
      if _available is None:
          _try_import_matplotlib()
  
      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: chainer/chainer/training/extensions/plot_report.py
imports: import json
  from os import path
  import warnings
  import numpy
  import six
  from chainer import reporter
  from chainer import serializer
  from chainer.training import extension
  from chainer.training import trigger
  from chainer.utils import argument
label_desc: Use image node_id 2 for calling a global function with example usage: _check_available() without return types