Save a pdf safely in python

save_pdf_with_qpdf.py

# https://github.com/mstamy2/PyPDF2/issues/53
import os, shutil, tempfile
from pathlib import Path
# Things from the subprocess module don't rely on the shell unless you
# explicitly ask for it and can accept a pre-split list of arguments,
# making calling subprocesses much safer.
# (If you really do need to split quoted stuff, use shlex.split() instead)
from subprocess import check_call

# [...]

# Use try/finally to ensure our cleanup code gets run
try:
    # There are a lot of ways to mess up creating temporary files in a way
    # that's free of race conditions, so just use mkdtemp() to safely
    # create a temporary folder that only we have permission to work inside
    # (We ask for it to be made in the same folder as filename because /tmp
    #  might be on a different drive, which would make the final overwrite
    #  into a slow "copy and delete" rather than a fast os.rename())
    tempdir = tempfile.mkdtemp(dir=SOURCE_FILE.parent)

    # I'm not sure if a qpdf failure could leave the file in a halfway
    # state, so have it write to a temporary file instead of reading from one
    temp_out= SOURCE_FILE.parent / f'qpdf_{SOURCE_FILE.name}'
    # Avoid the shell when possible and integrate with Python errors
    # (check_call() raises subprocess.CalledProcessError on nonzero exit
    check_call(['qpdf', "--password=", '--decrypt', SOURCE_FILE, temp_out])

    # I'm not sure if a qpdf failure could leave the file in a halfway
    # state, so write to a temporary file and then use os.rename to
    # overwrite the original atomically.
    # (We use shutil.move instead of os.rename so it'll fall back to a copy
    #  operation if the dir= argument to mkdtemp() gets removed)
    shutil.move(temp_out, SOURCE_FILE)
    print('File Decrypted (qpdf)')
finally:
    # Delete all temporary files
    shutil.rmtree(tempdir)