The python command line argument sys.argv is used as an example

#diff.py
#!/bin/env python
import sys 
if len(sys.argv) <> 3:
    print "Usage: " + sys.argv[0] + "file1 file2"
    sys.exit(-1)
file1 = sys.argv[1]
file2 = sys.argv[2]
list1 = {}
for line in open(file1):
    list1[line.split()[0]] = 1 
for line in open(file2):
    key = line.split()[0]
    if key not in list1:
        sys.stdout.write(line)