The right answer (using Python 2.7 and later, since check_output()
was introduced then) is:
py2output = subprocess.check_output(['python','py2.py','-i', 'test.txt'])
To demonstrate, here are my two programs:
py2.py:
import sys
print sys.argv
py3.py:
import subprocess
py2output = subprocess.check_output(['python', 'py2.py', '-i', 'test.txt'])
print('py2 said:', py2output)
Running it:
$ python3 py3.py
py2 said: b"['py2.py', '-i', 'test.txt']\n"
Here’s what’s wrong with each of your versions:
py2output = subprocess.check_output([str('python py2.py '),'-i', 'test.txt'])
First, str('python py2.py')
is exactly the same thing as 'python py2.py'
—you’re taking a str
, and calling str
to convert it to an str
. This makes the code harder to read, longer, and even slower, without adding any benefit.
More seriously, python py2.py
can’t be a single argument, unless you’re actually trying to run a program named, say, /usr/bin/python\ py2.py
. Which you’re not; you’re trying to run, say, /usr/bin/python
with first argument py2.py
. So, you need to make them separate elements in the list.
Your second version fixes that, but you’re missing the '
before test.txt'
. This should give you a SyntaxError
, probably saying EOL while scanning string literal
.
Meanwhile, I’m not sure how you found documentation but couldn’t find any examples with arguments. The very first example is:
>>> subprocess.check_output(["echo", "Hello World!"])
b'Hello World!\n'
That calls the "echo"
command with an additional argument, "Hello World!"
.
Also:
-i is a positional argument for argparse, test.txt is what the -i is
I’m pretty sure -i
is not a positional argument, but an optional argument. Otherwise, the second half of the sentence makes no sense.