How to use subprocess in a RxPY map correctly?

Question

I am trying to use RxPY to scan the IP to see which hosts are up.

However, currently it returns empty.

For ping(ip), if I simply return ip, it will return a list of IP address.

from reactivex import operators as ops
import reactivex as rx
import subprocess

# If I change to this version, it will return a list of IP address.
# def ping(ip):
#    return ip

def ping(ip):
    retval = subprocess.call(["ping", "-c1", "-n", "-i0.1", "-W1", ip])
    print("Here!")  # It never reached here.
    if retval == 0:
        return ip  # host is up
    else:
        return ""  # host is down


if __name__ == "__main__":
    ip_list = ["192.168.1.1", "192.168.1.2"]
    rx.of(ip_list).pipe(
        ops.map(lambda ip: ping(ip)),
    ).subscribe(lambda x: print(list(x)))

The line of subprocess.call is totally skipped.

I am thinking it might be related with async, however in this case, the function subprocess.call seems not an async function.

How to use subprocess correctly? Any guide would be appreciate!

Hongbo Miao · Accepted Answer · 2022-06-23T18:28:41.833

I found a solution. The idea is wrapping subprocess.call as an Observable.

After creating my custom operator based on the doc, now it works!

import reactivex as rx
import subprocess

def ping():
    def _ping(source):
        def subscribe(observer, scheduler=None):
            def on_next(ip):
                retval = subprocess.call(["ping", "-c1", "-n", "-i0.1", "-W1", ip])
                if retval == 0:  # host is up
                    observer.on_next(ip)
                else:  # host is down
                    observer.on_next("")

            return source.subscribe(
                on_next,
                observer.on_error,
                observer.on_completed)
        return rx.create(subscribe)
    return _ping

if __name__ == "__main__":
    ip_list = ['192.168.1.1', '192.168.1.2']
    rx.of(*ip_list).pipe(
        ping(),
    ).subscribe(lambda x: x)

It will print something like this now

PING 192.168.1.1 (192.168.1.1): 56 data bytes

--- 192.168.1.1 ping statistics ---
1 packets transmitted, 0 packets received, 100.0% packet loss
PING 192.168.1.2 (192.168.1.2): 56 data bytes

--- 192.168.1.2 ping statistics ---
1 packets transmitted, 0 packets received, 100.0% packet loss

How to use subprocess in a RxPY map correctly?

1 Answers1