code: def __testPeriod2Impl(self, maxLen):
      weights = [3, 2, 1]
      values = [1, 2, 3]
  
      wma = self.__buildWMA(weights, values, maxLen)
      self.assertEqual(wma[0], None)
      self.assertEqual(wma[1], None)
      self.assertEqual(
          wma[2], (1 * 3 + 2 * 2 + 3 * 1) / float(3 + 2 + 1)
      )
  
      self.assertEqual(len(wma.getDateTimes()), 3)
      for i in range(len(wma)):
          self.assertEqual(wma.getDateTimes()[i], None)
  
imports: from six.moves import xrange
  from .None import common
  from pyalgotrade.technical import ma
  from pyalgotrade import dataseries
  from pyalgotrade.barfeed import ninjatraderfeed
  from pyalgotrade import bar
label_desc: Use image node_id 3 for calling the WMATestCase obj's underlying member method code with example usage: obj.__testPeriod2Impl(maxLen) without return types