I want to run the following command from within a Python program:
python py2.py -i test.txt
I tried using subprocess.check_output as follows:
py2output = subprocess.check_output(['python py2.py', '-i', 'test.txt'])
py2output = subprocess.check_output(['python', 'py2.py', '-i', 'test.txt'])
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.