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POcommunicate() does not catch suprocess stdout
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copied!<pre><code>import subprocess def ExecuteAndGetValue(cmd, v): PrintCmd(cmd, v) sub = subprocess.Popen(cmd, shell = True, stdout=subprocess.PIPE) result = sub.communicate() sub.wait() return result import subprocess def ExecuteAndGetValue2(cmd, v): PrintCmd(cmd, v) sub = subprocess.Popen(cmd, shell = True, stdout=subprocess.PIPE) result = sub.communicate()[0] return result [aa, err] = Util.ExecuteAndGetValue(cmd, args.v) # run half an hour, the output size is about 15MB [bb, err] = Util.ExecuteAndGetValue(cmd, args.v) # run half an hour, the output size is about 15MB print aa // aa is empty print bb // bb is empty </code></pre> <p><code>cmd</code> prints/outputs: stderr using <code>print >> sys.stderr</code> and stdout using <code>print</code> </p> <pre><code>result = [] for i in range(n): print >> sys.stderr, "T_index: " + str(T_index) bb = func(i) result.append(bb) print '\n'.join(result) </code></pre> <p>cmd has a loop in which print <code>stderr</code> info. At the end, it prints all output to <code>result</code></p> <p>(1) if <code>cmd</code> print smaller size string, it works fine. <code>aa</code> and <code>bb</code> shows correct results.</p> <p>(2) if <code>cmd</code> print a large size such as 10 Mb, <code>aa</code> and <code>bb</code> are empty.</p> <p>(3) based on the above tests, it looks to me that sub.communicate()[0] read stdout from Popen in real time? if it is a large stdout, it cannot read it? Could someone explain it a little more ?</p> <p>In addition, I would like to see stderr or error message in screen in real time. If I use the following, it does not show stderr in real time:</p> <pre><code>import subprocess def ExecuteAndGetValue(cmd, v): PrintCmd(cmd, v) sub = subprocess.Popen(cmd, shell = True, stdout=subprocess.PIPE, stderr=subprocess.PIPE) result = sub.communicate() print result[1] return result </code></pre> <p>How can I fix this problem? it might be related to buffer size? Thanks </p>

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