Why QgsRasterCalculator crashes Qgis unexpectedly?

Question

I am struggling to sum some rasters using QgsRasterCalculator. When the step "calc.processCalculation()" is executed, QGIS crashes with a runtime error (R6025 - pure virtual function call) or a dump.

I have a list of raster paths generated in a for loop looking like the following one. Please tell me what do I do wrong and how could I make it work...

Here is my code:

from qgis.core import *
from PyQt4.QtCore import *
from qgis.analysis import QgsRasterCalculator, QgsRasterCalculatorEntry

s1 = "E:\rcalc\OUTPUT11.sdat"
s2 = "E:\rcalc\OUTPUT22.sdat"
s3 = "E:\rcalc\OUTPUT33.sdat"
list = [s1,s2,s3]

entries = []
formula = ""

for i in range(0, len(list)):
    raster = list[i]
    resp = QgsRasterLayer(raster)
    rast1 = QgsRasterCalculatorEntry()
    rast1.raster = resp
    rast1.ref = "rast"+str(i+1)
    rast1.bandNumber = 1
    entries.append(rast1)
    rast1 = None
    resp = None

    if(i == len(list)-1):
        formula = formula + 'rast'+str(i+1)  
    else:
        formula = formula + 'rast'+str(i+1)+' + '

resp = QgsRasterLayer(list[0])

calc = QgsRasterCalculator( formula, "E:\output.tif", 'GTiff', resp.extent(), resp.width(), resp.height(), entries )
calc.processCalculation()

Answer 1

I found the answer: When I replaced

resp = QgsRasterLayer(raster) 

with

resp = processing.getObject(raster)

The calculator worked fine.

In addition, the reference must have @ character to count the entries, so the line

rast1.ref = "rast"+str(i+1)

become

rast1.ref = "rast@"+str(i+1)

and the formula will be

rast@1 + rast@2 + rast@3 +...

When I used the formula

rast1 + rast2 + rast3

the result was a raster with a constant value of 6 (1+2+3). Hope my answer will be useful.