#!/usr/bin/env python3
#
# Limits the maximal virtual memory for a subprocess in Python.
#
# Linux only.
#

import subprocess
import resource

# Maximal virtual memory for subprocesses (in bytes).
MAX_VIRTUAL_MEMORY = 10 * 1024 * 1024 # 10 MB

def limit_virtual_memory():
    # The tuple below is of the form (soft limit, hard limit). Limit only
    # the soft part so that the limit can be increased later (setting also
    # the hard limit would prevent that).
    # When the limit cannot be changed, setrlimit() raises ValueError.
    resource.setrlimit(resource.RLIMIT_AS, (MAX_VIRTUAL_MEMORY, resource.RLIM_INFINITY))

p = subprocess.Popen(
    ['ls', '-l', '/'],
    # preexec_fn is a callable object that will be called in the child process
    # just before the child is executed.
    preexec_fn=limit_virtual_memory
)
p.communicate()