class_docstr: Class that creates a callable object that uses mouse clicks or key
  clicks on a figure window to place contour labels.
code: def pop_click(self, event, index=-1):
      self.button3(event)
  
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import six
  import matplotlib.lines
  import logging
label_desc: Use image node_id 3 for calling the BlockingContourLabeler obj's underlying member method code with example usage: obj.pop_click(event, index) without return types