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POquestion about pexpect in python
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copied!<p>I tried both pexpect and subprocess.Popen from python to call an external long term background process (this process use socket to communicate with external applications), with following details.</p> <ol> <li><p>subprocess.Popen(launchcmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE) This works fine. I do not need to do anything else. However, because I have to get the output immediately, I choose pexpect to avoid the pipe file buffer problem.</p></li> <li><p>obj= pexpect.spawn(launchcmd, timeout=None) after launching external process, I use a separate thread to do "readline" to read the output of the launched process "obj", and everything is ok.</p></li> <li><p>obj= pexpect.spawn(launchcmd, timeout=None) after launching external process, I did nothing further, i.e., just leave it there. Although, by using the "ps -e" command I can find the launched process, but the launched process seems blocked and cannot communicate in sockets with other applications. </p></li> </ol> <p>OK. To be more specific, I put some sample code to formulate my question.</p> <pre><code>import subprocess import pexpect import os t=1 while(True): if(t==1): background_process="./XXX.out" launchcmd = [background_process] #---option 3-------- p=pexpect.spawn(launchcmd, timeout=None) # process launced, problem with socket. #---option 1-------- p=subprocess.Popen(launchcmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE) # process launced, everything fine t=0 </code></pre> <p>Could anyone tell me what's wrong with the 3rd option? And if it is due to the fact that I did not use a separate thread to manipulate the output, why 1st option works with subprocess.popen? I suspect there is something wrong with pexpect to launch a process using socket, but I am not sure, especially considering option 2 works well.</p>

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