Optionally pass argument to subprocess in python

Question

In my script I call an executable with optional command line argument (if passed, this argument switches on a function in the executable, which is off by default). I want to control this option directly from argument of the script itself. Write now I do:

import subprocess option = False if option: check = subprocess.Popen(['executable', '--option']) else: check = subprocess.Popen(['executable'])

I tried to find a more compact way:

import subprocess option = False check = subprocess.Popen(['executable', '--option' if option else ''])

But this raises error "Unknown option" in the exactable itself.

And this raises error in python:

import subprocess option = False check = subprocess.Popen(['executable', '--option' if option else None])

So, my question: is there a way to pass an optional argument to subprocess in one line?

justintrudell · Accepted Answer · 2020-04-06 21:13:21Z

An alternative that's IMO more readable than the current suggestion is using list unpacking:

*(['--opt=val'] if opt else [])

And with your example:

check = subprocess.Popen([ 'executable', *(['--option'] if option else []) ])

falsetru · Accepted Answer · 2014-11-19 14:09:08Z

Using list slicing:

>>> ['executable', '--option'][:1 + False] ['executable'] >>> ['executable', '--option'][:1 + True] ['executable', '--option'] >>> False == 0 True >>> True == 1 True

check = subprocess.Popen(['executable', '--option'][:1 + option])

UPDATE Alternative

You can also use list * bool:

>>> ['a'] * True ['a'] >>> ['a'] * False []

Using this, you can combine multiple options:

check = subprocess.Popen(['executable'] + ['-option1'] * option1 + ['-option2'] * option2)

And if there are several such options (e.g. executable [--option1] [--option2] ...)?
@Roman, Assuming option variable is a boolean object, you can use alternative list * bool: subprocess.Popen(['executable'] + ['-option1'] * option1 + ['-option2'] * option2)

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