class_docstr: An order book update event.
class_docstr_tok: ["An","order","book","update","event","."]
docstr: Returns a list with the top 20 bid prices.
docstr_tok: ["Returns","a","list","with","the","top","20","bid","prices","."]
code: def getBidPrices(self):
      """Returns a list with the top 20 bid prices."""
      return [float(bid[0]) for bid in self.getData()["bids"]]
  
imports: import datetime
  from six.moves import queue
  from pyalgotrade.websocket import pusher
  from pyalgotrade.websocket import client
  from pyalgotrade.bitstamp import common
label_desc: Use image node_id 3 for calling the OrderBookUpdate obj's underlying member method code with example usage: obj.getBidPrices() and returns: unknown