Sorting a comma separated file according to the columns

sort_wrt_columns.py

#there are three columns. This script is gonna sort the file first w.r.t. column 3 then further w.r.t. column 2 
import csv

def getKey(item):
	return int(item[0])
def getKey1(item):
	return int(item[1])
def getKey2(item):
	return int(item[2])
	
	
cr=csv.reader(open('combine_work.txt','rb'))
output_file1=open('sorted_combine_work.txt','w+') 

all_elements=[]
for row in cr:
	all_elements.append(row)
all_elements=sorted(all_elements,key=getKey2)
all_elements=sorted(all_elements,key=getKey1)

for i in range(0,len(all_elements)):
	res=all_elements[i][0]+","+all_elements[i][1]+","+all_elements[i][2]+"\n"
	output_file1.write(res)