subprocess.call() in python is not producing files despite not producing an error

Question

I am using this script below, taken from here: https://github.com/theeko74/pdfc/blob/master/pdf_compressor.py

import os
import sys
import subprocess
def compress(input_file_path, output_file_path, power=0):
    """Function to compress PDF via Ghostscript command line interface"""
    quality = {
        0: '/default',
        1: '/prepress',
        2: '/printer',
        3: '/ebook',
        4: '/screen'
    }

    # Basic controls
    # Check if valid path
    if not os.path.isfile(input_file_path):
        print("Error: invalid path for input PDF file")
        sys.exit(1)

    # Check if file is a PDF by extension
    if input_file_path.split('.')[-1].lower() != 'pdf':
        print("Error: input file is not a PDF")
        sys.exit(1)

    print("Compress PDF...")
    initial_size = os.path.getsize(input_file_path)
    subprocess.Popen(['gs', '-sDEVICE=pdfwrite', '-dCompatibilityLevel=1.4',
                    '-dPDFSETTINGS={}'.format(quality[power]),
                    '-dNOPAUSE', '-dQUIET', '-dBATCH',
                    '-sOutputFile={}'.format(output_file_path),
                     input_file_path])

compress("D:/Documents/Pdf Handler/test.pdf","D:/Documents/Pdf Handler/testCompress.pdf")

I want to use it to compress a PDF, however when ever it was run the below error was produced:

Traceback (most recent call last):
  File "D:/Documents/Pdf Handler/compress.py", line 39, in <module>
    compress("D:/Documents/Pdf Handler/test.pdf","D:/Documents/Pdf Handler/testCompress.pdf")
  File "D:/Documents/Pdf Handler/compress.py", line 31, in compress
    input_file_path]
  File "C:\Python37\lib\subprocess.py", line 323, in call
    with Popen(*popenargs, **kwargs) as p:
  File "C:\Python37\lib\subprocess.py", line 775, in __init__
    restore_signals, start_new_session)
  File "C:\Python37\lib\subprocess.py", line 1178, in _execute_child
    startupinfo)
FileNotFoundError: [WinError 2] The system cannot find the file specified

After some research, i found out that i had to add shell=True in subprocess.call:

...
    print("Compress PDF...")
    initial_size = os.path.getsize(input_file_path)
    subprocess.Popen(['gs', '-sDEVICE=pdfwrite', '-dCompatibilityLevel=1.4',
                    '-dPDFSETTINGS={}'.format(quality[power]),
                    '-dNOPAUSE', '-dQUIET', '-dBATCH',
                    '-sOutputFile={}'.format(output_file_path),
                     input_file_path])

compress("D:/Documents/Pdf Handler/test.pdf","D:/Documents/Pdf Handler/testCompress.pdf")

whilst this did fix the issue of an error being raised, the code now doesn't appear to actually do anything. It runs, however no files are added to the specified directory.

Your help would be massively appreciated, as i mentioned i did take this code from elsewhere and the documentation is very sparse.

@mechanical_meat I'll attempt to re-do it without the spaces, i'll kick myself if that works though. — carbaretta, Apr 21 '20 at 23:18

score 0 · Answer 1 · answered Apr 21 '20 at 23:23

0

This isn't really an answer, but it's meant to help you debugging this.

You're currently flying blind, so you need to inspect the output of stdout and stderr like this:

import subprocess

proc = subprocess.Popen(['gs', '-sDEVICE=pdfwrite', '-dCompatibilityLevel=1.4',
                         '-dPDFSETTINGS={}'.format(quality[power]),
                         '-dNOPAUSE', '-dQUIET', '-dBATCH',
                         '-sOutputFile={}'.format(output_file_path),
                        input_file_path],shell=True,stdout=subprocess.PIPE,
                        stderr=subprocess.PIPE)
out, err = proc.communicate()
print(out)
print(err)

answered Apr 21 '20 at 23:23

mechanical_meat

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Okay i'll give that a shot now. would you mind explaining what stdout and stderr are/indicate? – carbaretta Apr 21 '20 at 23:25
Those are what the commands would return if you were executing this command in a shell. Since you're running it from a program those things are currently hidden. – mechanical_meat Apr 21 '20 at 23:26
Specifically if something is going wrong, it should be noted in `err` now. – mechanical_meat Apr 21 '20 at 23:26
This may be a silly question: do you have GhostScript installed on that machine? – mechanical_meat Apr 21 '20 at 23:35
yea i've installed it through the standard binary available on the website. The problem seems to be that "gs" is not recognized as a batch or internal command - is there something with environment variables i need to do? – carbaretta Apr 21 '20 at 23:48
Aha! You can follow the instructions here: https://stackoverflow.com/a/6015004/42346 – mechanical_meat Apr 21 '20 at 23:50

subprocess.call() in python is not producing files despite not producing an error

1 Answers1