Question about the example in the article Developing a Recursive Indicator (with a seed)

da zhang

When I run the example code in the article “Developing a Recursive Indicator (with a seed)”
https://www.backtrader.com/blog/posts/2018-01-27-recursive-indicators/recursive-indicator/
''''
import backtrader as bt

class EMA(bt.indicators.PeriodN):
params = {'period': 30} # even if defined, we can redefine the default value
lines = ('ema',) # our output line

def __init__(self):
    self.alpha = 2.0 / (1.0 + self.p.period)  # period -> exp smoothing factor

def nextstart(self):  # calculate here the seed value
    self.lines.ema[0] = self.data.get(size=self.p.period) / self.p.period

def next(self):
    ema1 = self.lines.ema[-1]  # previous EMA value
    self.lines.ema[0] = ema1 * (1.0 - self.alpha) + self.data[0] * self.alpha

''''
I met the following error
''''
File "C:/Bob_home/exploration/backtrader/data-pandas.py", line 50, in nextstart
self.lines.ema[0] = self.data.get(size=self.p.period) / self.p.period
TypeError: unsupported operand type(s) for /: 'array.array' and 'int'
''''

In the part of nextstart, from my understanding, ''''self.lines.ema[0] '''' is a digit, and ''''self.data.get(size=self.p.period) / self.p.period'''' is a series whose length is period.
why there exists the error? many thx.

backtrader

'''' is not ```

There is an obvious typo

@da-zhang said in Question about the example in the article Developing a Recursive Indicator (with a seed):

self.lines.ema[0] = self.data.get(size=self.p.period) / self.p.period
TypeError: unsupported operand type(s) for /: 'array.array' and 'int'

self.lines.ema[0] = sum(self.data.get(size=self.p.period)) / self.p.period