subprocess: deleting child processes in Windows

On Windows, subprocess.Popen.terminate calls win32's TerminalProcess. However, the behavior I see is that child processes of the process I am trying to terminate are still running. Why is that? How do I ensure all child processes started by the process are killed?

By using psutil:

import psutil, os

def kill_proc_tree(pid, including_parent=True):    
    parent = psutil.Process(pid)
    children = parent.children(recursive=True)
    for child in children:
        child.kill()
    gone, still_alive = psutil.wait_procs(children, timeout=5)
    if including_parent:
        parent.kill()
        parent.wait(5)

me = os.getpid()
kill_proc_tree(me)

Use taskkill with the /T flag

p = subprocess.Popen(...)
<wait>
subprocess.call(['taskkill', '/F', '/T', '/PID', str(p.pid)])

The flags to taskkill has the following docs:

TASKKILL [/S system [/U username [/P [password]]]]
         { [/FI filter] [/PID processid | /IM imagename] } [/T] [/F]

/S    system           Specifies the remote system to connect to.
/U    [domain\]user    Specifies the user context under which the
                       command should execute.
/P    [password]       Specifies the password for the given user
                       context. Prompts for input if omitted.
/FI   filter           Applies a filter to select a set of tasks.
                       Allows "*" to be used. ex. imagename eq acme*
/PID  processid        Specifies the PID of the process to be terminated.
                       Use TaskList to get the PID.
/IM   imagename        Specifies the image name of the process
                       to be terminated. Wildcard '*' can be used
                       to specify all tasks or image names.
/T                     Terminates the specified process and any
                       child processes which were started by it.
/F                     Specifies to forcefully terminate the process(es).
/?                     Displays this help message.

Or walk the process tree using comtypes and win32api:

def killsubprocesses(parent_pid):
    '''kill parent and all subprocess using COM/WMI and the win32api'''

    log = logging.getLogger('killprocesses')

    try:
        import comtypes.client
    except ImportError:
        log.debug("comtypes not present, not killing subprocesses")
        return

    logging.getLogger('comtypes').setLevel(logging.INFO)

    log.debug('Querying process tree...')

    # get pid and subprocess pids for all alive processes
    WMI = comtypes.client.CoGetObject('winmgmts:')
    processes = WMI.InstancesOf('Win32_Process')
    subprocess_pids = {} # parent pid -> list of child pids

    for process in processes:
        pid = process.Properties_('ProcessID').Value
        parent = process.Properties_('ParentProcessId').Value
        log.trace("process %i's parent is: %s" % (pid, parent))
        subprocess_pids.setdefault(parent, []).append(pid)
        subprocess_pids.setdefault(pid, [])

    # find which we need to kill
    log.debug('Determining subprocesses for pid %i...' % parent_pid)

    processes_to_kill = []
    parent_processes = [parent_pid]
    while parent_processes:
        current_pid = parent_processes.pop()
        subps = subprocess_pids[current_pid]
        log.debug("process %i children are: %s" % (current_pid, subps))
        parent_processes.extend(subps)
        processes_to_kill.extend(subps)

    # kill the subprocess tree
    if processes_to_kill:
        log.info('Process pid %i spawned %i subprocesses, terminating them...' % 
            (parent_pid, len(processes_to_kill)))
    else:
        log.debug('Process pid %i had no subprocesses.' % parent_pid)

    import ctypes
    kernel32 = ctypes.windll.kernel32
    for pid in processes_to_kill:
        hProcess = kernel32.OpenProcess(PROCESS_TERMINATE, FALSE, pid)
        if not hProcess:
            log.warning('Unable to open process pid %i for termination' % pid)
        else:
            log.debug('Terminating pid %i' % pid)                        
            kernel32.TerminateProcess(hProcess, 3)
            kernel32.CloseHandle(hProcess)