code: def _get_ema(cls, df, column, windows):
          
          window = cls.get_only_one_positive_int(windows)
          column_name = '{}_{}_ema'.format(column, window)
          if len(df[column]) > 0:
              df[column_name] = df[column].ewm(
                  ignore_na=False, span=window,
                  min_periods=0, adjust=True).mean()
          else:
              df[column_name] = []
docs: get exponential moving average
  
          :param df: data
          :param column: column to calculate
          :param windows: collection of window of exponential moving average
          :return: None