How to do a raster layer summation by loop?

[RebeccaRicker]

Hey folks,

I work with ArcGIS Pro and Python and I need to do a Summation over 31 raster layers. I want to do it by a loop, because I need it more often.

This is what I want to loop:

    arcpy.env.workspace = Folder_Single_Layer_ND_as_0

    Sum_Layer_ND_as_0 = \

    Raster("/offset_0_1.tif") \

    + Raster("/offset_0_2.tif") \

    + Raster("/offset_0_3.tif") \

    + Raster("/offset_0_4.tif") \

    + Raster("/offset_0_5.tif") \

    + Raster("/offset_0_6.tif") \

    + Raster("/offset_0_7.tif") \

    + Raster("/offset_0_8.tif") \

    + Raster("/offset_0_9.tif") \

    + Raster("/offset_0_10.tif") \

    + Raster("/offset_0_11.tif") \

    + Raster("/offset_0_12.tif") \

    + Raster("/offset_0_13.tif") \

    + Raster("/offset_0_14.tif") \

    + Raster("/offset_0_15.tif") \

    + Raster("/offset_0_16.tif") \

    + Raster("/offset_0_17.tif") \

    + Raster("/offset_0_18.tif") \

    + Raster("/offset_0_19.tif") \

    + Raster("/offset_0_20.tif") \

    + Raster("/offset_0_21.tif") \

    + Raster("/offset_0_22.tif") \

    + Raster("/offset_0_23.tif") \

    + Raster("/offset_0_24.tif") \

    + Raster("/offset_0_25.tif") \

    + Raster("/offset_0_26.tif") \

    + Raster("/offset_0_27.tif") \

    + Raster("/offset_0_28.tif") \

    + Raster("/offset_0_29.tif") \

    + Raster("/offset_0_30.tif") \

    + Raster("/offset_0_31.tif") \

    Sum_Layer_ND_as_0.save()

I tried so far...

    # Those are already definite

    # TxWx = "/offset"        # I need this as a Variable.

    # Number_of_Years = 31    # I calculated this from a NetCDF

...this:

    arcpy.env.workspace = Folder_Single_Layer_ND_as_0

    for Number in range(1, int(Number_of_Years))

        Sum_Layer_ND_as_0 += Raster(TxWx + "_0_" + Number + ".tif")

...and this:

    arcpy.env.workspace = Folder_Single_Layer_ND_as_0

    x = 1

    while True:

        Sum_Layer_ND_as_0 += Raster(TxWx + "_0_" + str(x) + ".tif")

        x += int(Number_of_Years)

... and this:

    arcpy.env.workspace = Folder_Single_Layer_ND_as_0

    count = 1

    while count <= int(Number_of_Years):

        Sum_Layer_ND_as_0 += Raster(TXWX + "_0_" + str(count) + ".tif")

        count +=1

Nothing works. I am a very beginner in Python. I would be very grateful if anyone could help me!!!

PS.: If my question is on the wrong position or I am not supposed to ask it here, please tell me.

[DanPatterson_Retired · Accepted solution]

https://community.esri.com/blogs/dan_patterson/2016/08/14/script-formatting to format your code so it is easier to read.

You need to use list rasters and sum the raster datasets using a Local sum

import arcpy
from arcpy import env
env.workspace = "C:/some_folder/a_folder_or_gdb"
arcpy.CheckOutExtension("Spatial")
in_rasters = arcpy.ListRasters("*", "TIF")  # change to suit the raster types
sum_cellstats = CellStatistics_sa(in_rasters, "SUM", "DATA")  # read the help!!
sum_cellstats.save("C:/test/output/sum_o_rama")‍‍‍‍‍‍‍

which has obviously not been tried but you can examine the various help topics to get the idea of how to work through through the process

[RebeccaRicker]

Thank you soooooo much again  

It worked!

[DanPatterson_Retired]

no problem