Get the output of lsof command Python 3.5 - linux

Question

I am trying to do a script that listen to a directory waiting to new files, then send to a Nextcloud. The files may be big ones,so I want to check if they are complete before sending. I thought about using lsof +D path/to/directory and check if the files are in the output of the command and send them when the file is not. The code would be something like:
command=list()
command.append("lsof")
command.append("+D")
command.append("/path/to/dir")
lsof = subprocess.check_output(command, stderr = subprocess.STDOUT)
But I get subprocess.CalledProcessError returned non-zero exit status 1
Can someone help to ecexute the command and get the output into the variable?
EDIT:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3.5/subprocess.py", line 626, in check_output
**kwargs).stdout
File "/usr/lib/python3.5/subprocess.py", line 708, in run
output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['lsof', '+D', '/home/CLI2Cache/sync']' returned non-zero exit status 1

Answer 1

There are couple of workarounds for this. You can use shell=True in the check_output -
lsof = subprocess.check_output(command, shell=True, stderr = subprocess.STDOUT)
Please note that shell=True is not safe as it also gives access to a lot of shell commands which might lead to some vulnerabilities if the command is user-specified or not sanitized properly. Please go through this to understand the risks.
A better way would be to use subprocess.Popen -
lsof = subprocess.Popen(command, stdout = subprocess.PIPE, stderr = subprocess.PIPE)
try:
output, errs = lsof.communicate(timeout=20)
except TimeoutExpired:
lsof.kill()
output, errs = proc.communicate()
communicate is also useful, if you want to send the input to the spawned process and get corresponding output at each step.