Use results of loop for another raster calculation

Question

I've been looking extensively to find a solution for what I think is a very simple exercise.

In general, I would like to know how I can extract a variable from a loop in Python and then use it elsewhere in the script. I've limited Python knowledge, however I know from R that this should be fairly simple. More specifically, my case is explained below.

I've two loops both multiplying rasters. I need to extract variables from each of the loops and then add them together.

import arcpy, os
from arcpy import env
from arcpy.sa import *
arcpy.CheckOutExtension("spatial")
arcpy.env.overwriteOutput = True
env.workspace = "D:/Join"
#
outputFolder = env.workspace
#
# A list of two different rasters
wheat = ["a_wheat", "b_wheat"]
for w in wheat:
 r_w=Times("landuse_w",w) # landuse is a raster
 r_w.save(os.path.join(outputFolder, "r_" + w ))
# This will generate r_a_wheat, r_b_wheat
barl = ["a_barl", "b_barl"]
for b in barl:
 r_b=Times("landuse_b",b)# landuse is a raster
 r_b.save(os.path.join(outputFolder, "r_" + b))
# This will generate r_a_barl, r_b_barl
# 
# Add rasters
add_a = r_a_wheat + r_a_barl
add_b = r_b_wheat + r_b_barl

The problem with the loops like this is that I need to save everything and then add up. I would prefer to extract from r_w the two rasters (r_a_wheat, r_b_wheat), do the same for r_b and then add up without having to save files. Is that possible?

• Hornbydd: With so few layers to process why go to the effort and add them to a list and cycle through those when you could simply reference them individually?
• egi007: I have 10 layers for each loop. I gave this as an example.
• Hornbydd: You should always explain the whole situation ;)

Answer 1

Now that you have described your problem in a bit more detail, why not cycle through the lists using their index number 0 to 9 pulling out the names, as it appears that you are pairing them.

Pseudo code:

wheat = ["a_wheat", "b_wheat","c_wheat"]
barl = ["a_barl", "b_barl","c_barl"]
for i in range(0,3,1):
 ras1 = wheat[i]
 ras2 = barl[i]
 print "processing " + ras1 + " & " + ras2
 r_w=Times("landuse_w",ras1)
 r_b=Times("landuse_b",ras2)
 add = r_w + r_b
 add.save("yourrastername")

• egi007: Thanks @Hornbydd! I don't want to add all rasters at the end. I need add_a = r_w_a + r_b_a; add_b = r_w_b + r_b_b; add_c = r_w_c + r_b_c That's why I thought of extracting the elements from loops and using them to add at the end.