(1) os.system
仅仅在一个子终端运行系统命令，而不能获取命令执行后的返回信息
system(command) -> exit_status
Execute the command (a string) in a subshell.如果再命令行下执行，结果直接打印出来
>>> os.system('ls')
04101419778.CHM bash document media py-django video
11.wmv books downloads Pictures python
all-20061022 Desktop Examples project tools(2) os.popen
该方法不但执行命令还返回执行后的信息对象
popen(command [, mode='r' [, bufsize]]) -> pipe
Open a pipe to/from a command returning a file object.例如：
>>>tmp = os.popen('ls *.py').readlines()
>>>tmp
Out[21]:
['dump_db_pickle.py ',
'dump_db_pickle_recs.py ',
'dump_db_shelve.py ',
'initdata.py ',
'__init__.py ',
'make_db_pickle.py ',
'make_db_pickle_recs.py ',
'make_db_shelve.py ',
'peopleinteract_query.py ',
'reader.py ',
'testargv.py ',
'teststreams.py ',
'update_db_pickle.py ',
'writer.py ']好处在于：将返回的结果赋于一变量，便于程序的处理。
(3) 使用模块 subprocess
>>> import subprocess
>>> subprocess.call(["cmd", "arg1", "arg2"],shell=True)获取返回和输出:
import subprocess
p = subprocess.Popen('ls', shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
for line in p.stdout.readlines():
print line,
retval = p.wait()(4) 使用模块 commands
>>> import commands
>>> dir(commands)
['__all__', '__builtins__', '__doc__', '__file__', '__name__', 'getoutput', 'getstatus','getstatusoutput', 'mk2arg', 'mkarg']
>>> commands.getoutput("date")
'Wed Jun 10 19:39:57 CST 2009'
>>>
>>> commands.getstatusoutput("date")
(0, 'Wed Jun 10 19:40:41 CST 2009')注意： 当执行命令的参数或者返回中包含了中文文字，那么建议使用subprocess，如果使用os.popen则会出现下面的错误:
Traceback (most recent call last):
File "./test1.py", line 56, inmain()
File "./test1.py", line 45, in main
fax.sendFax()
File "./mailfax/Fax.py", line 13, in sendFax
os.popen(cmd)
UnicodeEncodeError: 'ascii' codec can't encode characters in position 46-52: ordinal not inrange(128)
