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anaylzervwr may have something error

when I optimize a strategy,the vwr analyzer occur something error,it mainly in :
File "C:\Anaconda3\lib\sitepackages\backtrader\strategy.py", line 486, in _stop analyzer._stop() File "C:\Anaconda3\lib\sitepackages\backtrader\analyzer.py", line 200, in _stop self.stop() File "C:\Anaconda3\lib\sitepackages\backtrader\analyzers\vwr.py", line 154, in stop dt = pn / (pi * math.exp(ravg * n))  1.0 ZeroDivisionError: float division by zero
so,this value about pi * math.exp(ravg * n) may be zero, maybe we should change the code to :
def stop(self): super(VWR, self).stop() # Check if no value has been seen after the last 'dt_over' # If so, there is one 'pi' out of place and a None 'pn'. Purge if self._pns[1] is None: self._pis.pop() self._pns.pop() # Get results from children rs = self._returns.get_analysis() ravg = rs['ravg'] rnorm100 = rs['rnorm100'] # make n 1 based in enumerate (number of periods and not index) # skip initial placeholders for synchronization dts = [] for n, pipn in enumerate(zip(self._pis, self._pns), 1): pi, pn = pipn # add a more assert if pi * math.exp(ravg * n)!=0: dt = pn / (pi * math.exp(ravg * n))  1.0 else: dt = np.NaN dts.append(dt) sdev_p = standarddev(dts, bessel=True) vwr = rnorm100 * (1.0  pow(sdev_p / self.p.sdev_max, self.p.tau)) self.rets['vwr'] = vwr