piping with subprocess

[Peter Otten]

Rick Dooling wrote:

> On Saturday, February 1, 2014 6:54:09 AM UTC-6, Peter Otten wrote:

>> Try to convert the example from the above page
>> 
>> """
>> output=`dmesg | grep hda`
>> # becomes
>> p1 = Popen(["dmesg"], stdout=PIPE)
>> p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
>> p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
>> output = p2.communicate()[0]
>> """
>> 
>> to your usecase. Namely, replace
>> 
>> ["dmesg"] --> ["textutil", "-convert", "html", infile, "-stdout"]
>> ["grep", "hda"] --> ["pandoc", "-f", "html", "-t", "marktown", "-o",
>>                      outfile]
>> 
>> Don't forget to set
>> 
>> infile = ...
>> outfile = ...
>> 
>> to filenames (with absolute paths, to avoid one source of error).
>> If that doesn't work post the code you wrote along with the error
>> messages.
> 
> p1 = subprocess.Popen(["textutil", "-convert", "html", file],
> stdout=subprocess.PIPE) 
> p2 = subprocess.check_call(["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]
> 
> Errors
> 
> Traceback (most recent call last):
>   File "/Users/me/Python/any2pandoc.py", line 70, in <module>
>     convert_word_file(file, markdown_file)
>   File "/Users/me/Python/any2pandoc.py", line 59, in convert_word_file
>     output = p2.communicate()[0]
> AttributeError: 'int' object has no attribute 'communicate'
> 
> I get a markdown_file created but it's empty.

Well, you replaced the Popen() from the example with a check_call() which 
uses a Popen instance internally, but does not expose it. 

I recommend that you stick as closely to the example as possible until you 
have a working baseline version. I'd try

textutil = subprocess.Popen(
    ["textutil", "-convert", "html", file], 
    stdout=subprocess.PIPE)
pandoc = subprocess.Popen(
    ["pandoc", "-f", "html", "-t", "markdown", "-o", markdown_file],
    stdin=textutil.stdout)

textutil.stdout.close()
pandoc.communicate()