execfile('helloworld.py')

自2.6：popen后弃用

import os
os.popen('python helloworld.py') # Just run the program
os.popen('python helloworld.py').read() # Also gets you the stdout

预先使用：subprocess

import subprocess
subprocess.call(['python','helloworld.py']) # Just run the program
subprocess.check_output(['python','helloworld.py']) # Also gets you the stdout

阅读文档的详细信息:-)