Python 3.8: How does one pass a variable to a Windows CMD subprocess?

Question

Up front confession... I'm a python neophyte. Please forgive any ignorance on my part.

As just a way to learn more, I'm trying to write a script that will take my latest Quicken backup and with 7-Zip, create a compressed and encrypted file with a timestamp in the name. I then want to copy it two two locations.

I have succeeded up the the name part. I've created a variable for the time the script starts and I want to append this to a base file name, but I don't seem to be able to do it. When I've tried, the script runs, but nothing is ever created, no compressed file that is. If I remove what I have with regard to the variable for the filename, I do get a compressed and encrypted file as expected.

Here is what I have so far. The print commands are just there for me making sure I've done the 'today' and 'newfile' variables correctly. Also, I'm doing the testing with just an empty .docx file so that it processes quicker.

Thanks in advance for any/all help or suggestions. I really appreciate it.

from datetime import datetime
from pathlib import Path

today = datetime.now()
print(today.strftime('%Y-%m-%d %H:%M:%S'))
newfile = 'Q2020_' + (today.strftime('%m-%d-%Y_%H%M%S'))
print(newfile)

os.chdir('D:/Quicken Backups')
print(os.getcwd())


import subprocess
cmd= ['C:\\Program Files\\7-Zip\\7z.exe', 'a', '-t7z', '-mx9', '"D:\\Quicken Backups\\Quicken2020\\" + newfile ".7z"', '-ppassword', '-mhe', 'D:\\Quicken Backups\\test.docx']
subprocess.Popen(cmd, stderr=subprocess.STDOUT, stdout=subprocess.PIPE)

Answer 1

Have you thought about using a python package made for zipping, like zipfile ?

This way you dont need to deal with opening a subprocess

import zipfile

dest_zip_folder = '2020_backup.zip'   # new file name
file_to_zip = 'D:\\Quicken Backups\\test.docx'
zipfile.ZipFile(dest_zip_folder, mode='w').write(file_to_zip)

If you dont want to use that way, I see an error in your code.

You are missing a + after newfile

cmd = [ ...., .... + newfile + '.7zip', ... ]

Also give subprocess.call() a try

import subproccess
cmd = [. . . . . .]
subprocess.call(cmd)

Answer 2

It took a LOT of mucking around with Windows variables syntax and running the subprocess a little differently, but I finally got the thing working, outputting an encrypted file with a date/time stamp in the file name.

For troubleshooting I added the /K to the cmd command so that the window would not close upon completion. This was a HUGE help in trouble shooting this.

Thanks to everyone who even looked at my posted. I hope someday this thread will help someone else!

import os
from pathlib import Path

os.chdir('D:/Quicken Backups')
print(os.getcwd())

import subprocess
cmd = subprocess.Popen('cmd.exe /K ""C:\\Program Files\\7-Zip\\7z.exe" a -t7z -mx9 "D:\\Quicken Backups\\Quicken2020\\Q2020_%DATE:~4,2%-%DATE:~7,2%-%DATE:~-4%_%TIME:~0,2%%TIME:~3,2%%TIME:~8%.7z" -ppassword -mhe "D:\\Quicken Backups\\test.docx"')