class_docstr: Exponential Moving Average filter.
  
  :param dataSeries: The DataSeries instance being filtered.
  :type dataSeries: :class:`pyalgotrade.dataseries.DataSeries`.
  :param period: The number of values to use to calculate the EMA. Must be an integer greater than 1.
  :type period: int.
  :param maxLen: The maximum number of values to hold.
      Once a bounded length is full, when new items are added, a corresponding number of items are discarded from the
      opposite end. If None then dataseries.DEFAULT_MAX_LEN is used.
  :type maxLen: int.
code: def __init__(self, dataSeries, period, maxLen=None):
      super(EMA, self).__init__(
          dataSeries, EMAEventWindow(period), maxLen
      )
  
imports: import numpy
  from pyalgotrade import technical
label_desc: Use image node_id 1 to create a new EMA object from inherited base classes: technical with example: obj = EMA(dataSeries, period, maxLen)