code: def read_counts(node):
    
    cfg.forward(node, cfg.ReachingDefinitions())
  
    rc = ReadCounts()
    rc.visit(node)
    return rc.n_read
docs: Check how many times a variable definition was used.
  
    Args:
      node: An AST to analyze.
  
    Returns:
      A dictionary from assignment nodes to the number of times the assigned to
          variable was used.