class_docstr: Fixed-size NumPy array ring buffer
code: def __getitem__(self, key):
      return self.buffer[key]
  
imports: import time, sys, os
  from Qt import QtCore
  import numpy
  from qspectrumanalyzer.utils import smooth
  from qspectrumanalyzer.backends import soapy_power
label_desc: Use image node_id 4 for calling the HistoryBuffer obj's underlying member method code with example usage: obj.__getitem__(key) and returns: self