subprocess细节

pipe = Popen([cmd] , executable=cmd, stdout=PIPE, stderr=PIPE,stdin=PIPE)
如果需要让子进程输入数据的话需要指明stdin的输入为管道
Popen.communicate(input=None) 

Interact with process: Send data to stdin. Read data from stdout and stderr, 
until end-of-file is reached. Wait for process to terminate. The optional 
input argument should be a string to be sent to the child process, or 
None, if no data 
should be sent to the child.
 returns a tuple (stdoutdata, stderrdata).这个方法的作用就是为了通讯！即父子进程之间的管道是基于这个进行通讯的！所以可以这样做：def run_exe(fail_if_stderr=False, encoding="utf-8"):    cmd = find_program("csystem.exe")    pipe = Popen([cmd] , executable=cmd, stdout=PIPE, stderr=PIPE,stdin=PIPE)    time.sleep(5)    out, err = pipe.communicate('0\n')