python - kill a process by its name

#a python script to kill process by its name
# kill_process.py
import os, signal

def check_kill_process(pstring):
    for line in os.popen("ps ax | grep " + pstring + " | grep -v grep"):
        fields = line.split()
        pid = fields[0]
        os.kill(int(pid), signal.SIGKILL)