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Subject: Re: Using Python instead of Bash
From: Cem Karan <cfkaran2@gmail.com>
In-Reply-To: <87h9qsnckl.fsf@Equus.decebal.nl>
Date: Sun, 31 May 2015 10:14:29 -0400
Cc: python-list@python.org
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> I help someone that has problems reading. For this I take photo's of
> text, use convert from ImageMagick to make a good contrast (original
> paper is grey) and use lpr to print it a little bigger.
>=20
> Normally I would implement this in Bash, but I thought it a good idea
> to implement it in Python. This is my first try:
>    import glob
>    import subprocess
>=20
>    treshold =3D 66
>    count =3D 0
>    for input in sorted(glob.glob('*.JPG')):
>        count +=3D 1
>        output =3D '{0:02d}.png'.format(count)
>        print('Going to convert {0} to {1}'.format(input, output))
>        p =3D subprocess.Popen(['convert', '-threshold', =
'{0}%'.format(treshold), input, output])
>        p.wait()
>        print('Going to print {0}'.format(output))
>        p =3D subprocess.Popen(['lpr', '-o', 'fit-to-page', '-o', =
'media=3DA4', output])
>        p.wait()
>=20
> There have to be some improvements: display before printing,
> possibility to change threshold, =85 But is this a good start, or =
should
> I do it differently?


As a first try, I think its pretty good, but to really answer your =
question, I think we could use a little more information. =20

- Are you using python 2, or python 3?  There are slightly easier ways =
to do this using concurrent.futures objects, but they are only available =
under python 3. (See =
https://docs.python.org/3/library/concurrent.futures.html)

- In either case, subprocess.call(), subprocess.check_call(), or =
subprocess.check_output() may be easier to use.  That said, your code is =
perfectly fine!  The only real difference is that subprocess.call() will =
automatically wait for the call to complete, so you don't need to use =
p.wait() from above.  (See =
https://docs.python.org/2.7/library/subprocess.html, and =
https://docs.python.org/3/library/subprocess.html)=20



The following codes does the conversion in parallel, and submits the =
jobs to the printer serially.  That should ensure that the printed =
output is also in sorted order, but you might want to double check =
before relying on it too much.  The major problem with it is that you =
can't display the output before printing; since everything is running in =
parallel, you'll have race conditions if you try.  **I DID NOT TEST THIS =
CODE, I JUST TYPED IT OUT IN MY MAIL CLIENT!**  Please test it carefully =
before relying on it!

"""
import subprocess
import concurrent.futures
import glob
import os.path

_THRESHOLD =3D 66

def _collect_filenames():
    files =3D glob.glob('*.JPG')

    # I build a set of the real paths so that if you have=20
    # symbolic links that all point to the same file, they
    # they are automatically collapsed to a single file
    real_files =3D {os.path.realpath(x) for x in files}
    base_files =3D [os.path.splitext(x)[0] for x in real_files]
    return base_files

def _convert(base_file_name):
    """
    This code is slightly different from your code.  Instead
    of using numbers as names, I use the base name of file and
    append '.png' to it.  You may need to adjust this to ensure
    you don't overwrite anything.
    """
    input =3D base_file_name + ".JPG"
    output =3D base_file_name + ".png"
    subprocess.call(['convert', '-threshold', '{0}%'.format(_THRESHOLD), =
input, output])

def _print_files_in_order(base_files):
    base_files.sort()
    for f in base_files:
        output =3D f + ".png"
        subprocess.call(['lpr', '-o', 'fit-to-page', '-o', 'media=3DA4', =
output])

def driver():
    base_files =3D _collect_filenames()

    # If you use an executor as a context manager, then the
    # executor will wait until all of the submitted jobs finish
    # before it returns.  The submitted jobs will execute in
    # parallel.
    with concurrent.futures.ProcessPoolExecutor() as executor:
        for f in base_files:
            executor.submit(_convert_and_print, f)

    _print_files_in_order(base_files)
"""

Thanks,
Cem Karan=