Scenes (scenarios, user stories, ...) of program execution with Python.
<insert hangman picture here>
Core Subprocess "features" to watch for:
child exception propagation if executing Python script (http://docs.python.org/2/library/subprocess.html#exceptions)
- check_call() or check_output() return exception on non-zero exit code (other functions do not)
Fire and Forget
Crossplatform shell automation
I am a user, who tired of writing shell commands by hand, and wants a crossplatform way of executing them on Window/Linux/Mac OS. I don't care about security - I am my own evil Pinocchio.
1. "i only care that the program is successfully started"
- execute the command
- get the signal that it is successfully started (no 'command not found' error)
- detach and let the process live its own live
type of command argument affects crossplatform behavior
[ ] here should be a table of shell=True, typeof(command), unix, windows, mac os
- child Python exceptions: affected|unaffected
Libraries on Execution
http://amoffat.github.com/sh/ - avoids suprocess altogether, linux-only for now
Notes about bad design in subprocess
check_call() or check_output() are shortcuts for executing Popen calls (convenience functions), but they modify the error handling behavior, leading to new exceptions when return codes are not the same. There is a also a call() helper that doesn't add new exceptions in this case and repeats Popen behaviour. This is what is called "inconsistent design" of API.
The check_* in the names of the helpers is probably because of those added exceptions, but that's not obvious. Names became non-friendly for humans. There might be a good rational user story behind this change, but it is missing in the context of this API, so as a user, I don't have a chance to memorize the conditions, when this can be handy. Defining the conditions is the goal of writing this page.