class_docstr: source of buffered demonstration data 
class_docstr_tok: ["source","of","buffered","demonstration","data"]
docstr: prepare, but don't start yet 
docstr_tok: ["prepare",",","but","do","n't","start","yet"]
code: def __init__(
      self,
      sample_rate=200.0,
      signal_period=0.55,
      negative_period=None,
      max_length=300,
  ):
      """prepare, but don't start yet"""
      self.rate = sample_rate
      self.period = signal_period
      self.neg_period = negative_period
      self.start_time = 0.0
      self.sample_idx = 0
  
file_path: pyqtgraph/pyqtgraph/examples/ColorGradientPlots.py
imports: import time
  import numpy
  import pyqtgraph
  from pyqtgraph.Qt import QtCore, mkQApp
label_desc: Use image node_id 1 to create a new DataSource object from inherited base classes: object with example: obj = DataSource(sample_rate, signal_period, negative_period, max_length)