class_docstr: Shows the difference between a short and long exponential moving
  averages expressed in percentage. The MACD does the same but expressed in
  absolute points.
  
  Expressing the difference in percentage allows to compare the indicator at
  different points in time when the underlying value has significatnly
  different values.
  
  Formula:
    - po = 100 * (ema(short) - ema(long)) / ema(long)
  
  See:
    - http://stockcharts.com/school/doku.php?id=chart_school:technical_indicators:price_oscillators_ppo
code: def __init__(self):
      super(PercentagePriceOscillator, self).__init__()
  
      den = self.ma2 if self._long else self.ma1
  
      self.lines.ppo = 100.0 * self.lines[0] / den
      self.l.signal = self.p._movav(
          self.l.ppo, period=self.p.period_signal
      )
      self.lines.histo = self.lines.ppo - self.lines.signal
  
file_path: backtrader/backtrader/indicators/priceoscillator.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from .None import Indicator, Max, MovAv
label_desc: Use image node_id 1 to create a new PercentagePriceOscillator object from inherited base classes: _PriceOscBase with example: obj = PercentagePriceOscillator()