class_docstr: xml filter that insert a subplot
docstr: Generate data
docstr_tok: ["Generate","data"]
code: def __init__(self, a, b):
      """Generate data"""
      self.data = [b[i] - a[i] for i in range(len(a))]
  
imports: from pygal import Bar
label_desc: Use image node_id 1 to create a new ChangeBarsXMLFilter object from inherited base classes: object with example: obj = ChangeBarsXMLFilter(a, b)