Run an executable, wait for it to produce output, run another program

Question

Within a Python script, I'm trying to execute the following sequence of events:

1. Open a command window and run a program. When it completes, it outputs a text file.
2. Once that text file has been created, close the program.
3. After that has happened, run a new program using the text file as an input

Here's what I have so far:

subprocess.popen(['cmd','/c',r'programThatRuns.exe'])
subprocess.wait()  # ? subprocess.check_call()? kill?
subprocess.popen(['cmd','/c',r'otherProgramThatRuns.exe'])

So I guess I'm really stuck on the second line

Answer 1

I think all you need is:

subprocess.check_call(['programThatRuns.exe'])
subprocess.check_call(['otherProgramThatRuns.exe'])

The check_call function will run the program and wait for it to finish. If it fails (non-0 exit code) it will throw a CalledProcessError exception.

You generally don't want to run programs through cmd, just run them directly. You only need to force using cmd if the program isn't an executable, e.g. for a builtin command like dir, for a .bat or .cmd file, or if you want to use file associations.

Answer 2

Have you tried using subprocess.call?

Python 2 - Python 3

Run the command described by args. Wait for command to complete, then return the returncode attribute.

Seems to be what you're trying to do. Simply run the first process, check that the file exists, and pass the file into the second process to use.

subprocess.check_call will also work for what you're trying to do, except that if the process returns a non-zero return code it'll raise an exception while call will simply return the return code.