$ cat nani123.py 
#!/usr/bin/env python

input = open("temp.txt", 'r')

for line in input:

    line = line.rstrip()
    line = line.split(',')
    num = line[0]
    data = line[1:]

    while data:
        print num + "," + ','.join(data[:3])
        data = data[3:]

$ cat temp.txt 
1,a,b,c,d,e,f,g,h
2,f,g,h,i,l


$ python nani123.py 
1,a,b,c
1,d,e,f
1,g,h
2,f,g,h
2,i,l