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POstdout Won't Flush After Exception
 

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    <p>I have the following Python code:</p> <pre><code>import sys import traceback fifo_in = sys.argv[1] while 1: try: exec open(fifo_in) except: traceback.print_exc() sys.stdout.flush() </code></pre> <p>The first argument is a named pipe created by <code>mkfifo</code>. So the following prints '1':</p> <pre><code>mkfifo input python script.py input ... in a separate terminal ... echo "print 1" &gt; input </code></pre> <p>Great, so far so good. But when I do something like <code>echo "foobar" &gt; input</code>, the script only prints <em>part</em> of the traceback. It then pauses until I send it another command, and the output gets all mixed up:</p> <pre><code>echo "asdf" &gt; input # pause here and check output echo "print 1" &gt; input ... in output terminal ... Traceback (most recent call last): File "test.py", line 8, in &lt;module&gt; exec open(fifo_in) File "in", line 1, in &lt;module&gt; ...PAUSES HERE... print 1 NameError: name 'asdf' is not defined </code></pre> <p>What's going on? How can I get stdout to flush fully and why is it out of order? I've tried using <code>traceback.format_exc</code> instead, then printing it by hand, but I get the same result. Calling <code>sys.stderr.flush</code> does not fix anything either. I've also tried putting a sleep in the loop to see if that helps, but nothing.</p> <p><strong>UPDATE</strong></p> <p>One interesting piece of behavior I am seeing: If I <code>ctrl+c</code> it, normally the program keeps running - the try/except just catches the <code>KeyboardInterrupt</code> and it keeps looping. However, if I <code>ctr+c</code> it after sending it an error, the program exits and I get the following. It's almost like it pauses inside of <code>print_exc</code>:</p> <pre><code>^CTraceback (most recent call last): File "test.py", line 10, in &lt;module&gt; traceback.print_exc() File "/usr/lib/python2.7/traceback.py", line 232, in print_exc print_exception(etype, value, tb, limit, file) File "/usr/lib/python2.7/traceback.py", line 125, in print_exception print_tb(tb, limit, file) File "/usr/lib/python2.7/traceback.py", line 69, in print_tb line = linecache.getline(filename, lineno, f.f_globals) File "/usr/lib/python2.7/linecache.py", line 14, in getline lines = getlines(filename, module_globals) File "/usr/lib/python2.7/linecache.py", line 40, in getlines return updatecache(filename, module_globals) File "/usr/lib/python2.7/linecache.py", line 132, in updatecache with open(fullname, 'rU') as fp: KeyboardInterrupt </code></pre>
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    1. PO
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      1. PTAnswer
    1. This table or related slice is empty.
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    1. USdave mankoff
    1. USdave mankoff
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    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
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      1. POstdout Won't Flush After Exception
      1. This table or related slice is empty.
      1. VTUpMod
    1. COWouldn't you want the flush to be in your except block ?
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      1. USHunter McMillen
    2. CO@HunterMcMillen I want it to flush no matter what path the code takes. Putting a second flush inside the except block doesn't seem to help.
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      1. POstdout Won't Flush After Exception
      1. USdave mankoff
    3. COIt might be worth trying it out with the `flush` call in a `finally` block. I am not sure if it will work in this particular case, but I believe this type of situation is one of the reasons `finally` exists.
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      1. POstdout Won't Flush After Exception
      1. USbernie
 

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