piping with subprocess

Rick Dooling rpdooling at gmail.com
Sat Feb 1 15:00:59 CET 2014


On Saturday, February 1, 2014 7:54:34 AM UTC-6, Rick Dooling wrote:
> On Saturday, February 1, 2014 6:54:09 AM UTC-6, Peter Otten wrote:
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> > Rick Dooling wrote:
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> > > I spent half a day trying to convert this bash script (on Mac)
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> > > 
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> > > textutil -convert html $1 -stdout | pandoc -f html -t markdown -o $2
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> > > 
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> > > into Python using subprocess pipes.
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> > > It works if I save the above into a shell script called convert.sh and
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> > > then do
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> > > subprocess.check_call(["convert.sh", file, markdown_file])
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> > > 
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> > > where file and markdown_file are variables.
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> > > 
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> > > But otherwise my piping attempts fail.
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> > It is always a good idea to post your "best effort" failed attempt, if only 
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> > to give us an idea of your level of expertise.
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> > > Could someone show me how to pipe in subprocess. Yes, I've read the doc,
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> > > especially
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> > > http://docs.python.org/2/library/subprocess.html#replacing-shell-pipeline
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> > > 
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> > > But I'm a feeble hobbyist, not a computer scientist.
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> > Try to convert the example from the above page
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> > """
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> > output=`dmesg | grep hda`
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> > # becomes
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> > p1 = Popen(["dmesg"], stdout=PIPE)
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> > 
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> > p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
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> > p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
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> > output = p2.communicate()[0]
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> > """
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> > to your usecase. Namely, replace
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> > ["dmesg"] --> ["textutil", "-convert", "html", infile, "-stdout"]
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> > ["grep", "hda"] --> ["pandoc", "-f", "html", "-t", "marktown", "-o",
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> >                      outfile]
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> > Don't forget to set
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> > infile = ... 
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> > outfile = ... 
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> > to filenames (with absolute paths, to avoid one source of error).
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> > If that doesn't work post the code you wrote along with the error messages.
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> 
> 
> p1 = subprocess.Popen(["textutil", "-convert", "html", file], stdout=subprocess.PIPE)
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> p2 = subprocess.check_call(["pandoc", "-f", "html", "-t", "markdown", "-o", markdown_file], stdin=p1.stdout, stdout=subprocess.PIPE)
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> p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
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> output = p2.communicate()[0]
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> 
> Errors
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> Traceback (most recent call last):
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>   File "/Users/me/Python/any2pandoc.py", line 70, in <module>
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>     convert_word_file(file, markdown_file)
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>   File "/Users/me/Python/any2pandoc.py", line 59, in convert_word_file
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>     output = p2.communicate()[0]
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> AttributeError: 'int' object has no attribute 'communicate'
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> 
> 
> I get a markdown_file created but it's empty.
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> Thanks,
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> RD
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> ps - Daniel's works fine but I still don't learn to pipe :)

Okay, sorry. I fixed that obvious goof

    p1 = subprocess.Popen(["textutil", "-convert", "html", file], stdout=subprocess.PIPE)
    p2 = subprocess.Popen(["pandoc", "-f", "html", "-t", "markdown", "-o", markdown_file], stdin=p1.stdout, stdout=subprocess.PIPE)
    p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
    output = p2.communicate()[0]

Now I get no errors, but I still get a blank markdown file.



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